Merge branch 'perfcounters-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perfcounters-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (574 commits)
  perf_counter: Turn off by default
  perf_counter: Add counter->id to the throttle event
  perf_counter: Better align code
  perf_counter: Rename L2 to LL cache
  perf_counter: Standardize event names
  perf_counter: Rename enums
  perf_counter tools: Clean up u64 usage
  perf_counter: Rename perf_counter_limit sysctl
  perf_counter: More paranoia settings
  perf_counter: powerpc: Implement generalized cache events for POWER processors
  perf_counters: powerpc: Add support for POWER7 processors
  perf_counter: Accurate period data
  perf_counter: Introduce struct for sample data
  perf_counter tools: Normalize data using per sample period data
  perf_counter: Annotate exit ctx recursion
  perf_counter tools: Propagate signals properly
  perf_counter tools: Small frequency related fixes
  perf_counter: More aggressive frequency adjustment
  perf_counter/x86: Fix the model number of Intel Core2 processors
  perf_counter, x86: Correct some event and umask values for Intel processors
  ...

10 files changed, 4377 insertions, 11 deletions

diff --git a/kernel/Makefile b/kernel/Makefile
index a35eee3436de..90b53f6dc226 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -96,6 +96,7 @@ obj-$(CONFIG_TRACING) += trace/
 obj-$(CONFIG_X86_DS) += trace/
 obj-$(CONFIG_SMP) += sched_cpupri.o
 obj-$(CONFIG_SLOW_WORK) += slow-work.o
+obj-$(CONFIG_PERF_COUNTERS) += perf_counter.o
 
 ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y)
 # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is
diff --git a/kernel/exit.c b/kernel/exit.c
index 51d1fe3fb7ad..b6c90b5ef509 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -48,6 +48,7 @@
 #include <linux/tracehook.h>
 #include <linux/fs_struct.h>
 #include <linux/init_task.h>
+#include <linux/perf_counter.h>
 #include <trace/events/sched.h>
 
 #include <asm/uaccess.h>
@@ -154,6 +155,9 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
 {
         struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
 
+#ifdef CONFIG_PERF_COUNTERS
+        WARN_ON_ONCE(tsk->perf_counter_ctxp);
+#endif
         trace_sched_process_free(tsk);
         put_task_struct(tsk);
 }
@@ -170,6 +174,7 @@ repeat:
         atomic_dec(&__task_cred(p)->user->processes);
 
         proc_flush_task(p);
+
         write_lock_irq(&tasklist_lock);
         tracehook_finish_release_task(p);
         __exit_signal(p);
@@ -971,16 +976,19 @@ NORET_TYPE void do_exit(long code)
                 module_put(tsk->binfmt->module);
 
         proc_exit_connector(tsk);
+
+        /*
+         * Flush inherited counters to the parent - before the parent
+         * gets woken up by child-exit notifications.
+         */
+        perf_counter_exit_task(tsk);
+
         exit_notify(tsk, group_dead);
 #ifdef CONFIG_NUMA
         mpol_put(tsk->mempolicy);
         tsk->mempolicy = NULL;
 #endif
 #ifdef CONFIG_FUTEX
-        /*
-         * This must happen late, after the PID is not
-         * hashed anymore:
-         */
         if (unlikely(!list_empty(&tsk->pi_state_list)))
                 exit_pi_state_list(tsk);
         if (unlikely(current->pi_state_cache))
diff --git a/kernel/fork.c b/kernel/fork.c
index bb762b4dd217..4430eb1376f2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -62,6 +62,7 @@
 #include <linux/blkdev.h>
 #include <linux/fs_struct.h>
 #include <linux/magic.h>
+#include <linux/perf_counter.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -1096,6 +1097,10 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         /* Perform scheduler related setup. Assign this task to a CPU. */
         sched_fork(p, clone_flags);
 
+        retval = perf_counter_init_task(p);
+        if (retval)
+                goto bad_fork_cleanup_policy;
+
         if ((retval = audit_alloc(p)))
                 goto bad_fork_cleanup_policy;
         /* copy all the process information */
@@ -1290,6 +1295,7 @@ bad_fork_cleanup_semundo:
 bad_fork_cleanup_audit:
         audit_free(p);
 bad_fork_cleanup_policy:
+        perf_counter_free_task(p);
 #ifdef CONFIG_NUMA
         mpol_put(p->mempolicy);
 bad_fork_cleanup_cgroup:
@@ -1403,6 +1409,12 @@ long do_fork(unsigned long clone_flags,
                 if (clone_flags & CLONE_VFORK) {
                         p->vfork_done = &vfork;
                         init_completion(&vfork);
+                } else if (!(clone_flags & CLONE_VM)) {
+                        /*
+                         * vfork will do an exec which will call
+                         * set_task_comm()
+                         */
+                        perf_counter_fork(p);
                 }
 
                 audit_finish_fork(p);
diff --git a/kernel/mutex.c b/kernel/mutex.c
index e5cc0cd28d54..947b3ad551f8 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -89,7 +89,7 @@ __mutex_lock_slowpath(atomic_t *lock_count);
  *
  * This function is similar to (but not equivalent to) down().
  */
-void inline __sched mutex_lock(struct mutex *lock)
+void __sched mutex_lock(struct mutex *lock)
 {
         might_sleep();
         /*
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
new file mode 100644
index 000000000000..ef5d8a5b2453
--- /dev/null
+++ b/kernel/perf_counter.c
@@ -0,0 +1,4260 @@
+/*
+ * Performance counter core code
+ *
+ *  Copyright (C) 2008 Thomas Gleixner <tglx@linutronix.de>
+ *  Copyright (C) 2008-2009 Red Hat, Inc., Ingo Molnar
+ *  Copyright (C) 2008-2009 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
+ *
+ *  For licensing details see kernel-base/COPYING
+ */
+
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/smp.h>
+#include <linux/file.h>
+#include <linux/poll.h>
+#include <linux/sysfs.h>
+#include <linux/dcache.h>
+#include <linux/percpu.h>
+#include <linux/ptrace.h>
+#include <linux/vmstat.h>
+#include <linux/hardirq.h>
+#include <linux/rculist.h>
+#include <linux/uaccess.h>
+#include <linux/syscalls.h>
+#include <linux/anon_inodes.h>
+#include <linux/kernel_stat.h>
+#include <linux/perf_counter.h>
+
+#include <asm/irq_regs.h>
+
+/*
+ * Each CPU has a list of per CPU counters:
+ */
+DEFINE_PER_CPU(struct perf_cpu_context, perf_cpu_context);
+
+int perf_max_counters __read_mostly = 1;
+static int perf_reserved_percpu __read_mostly;
+static int perf_overcommit __read_mostly = 1;
+
+static atomic_t nr_counters __read_mostly;
+static atomic_t nr_mmap_counters __read_mostly;
+static atomic_t nr_comm_counters __read_mostly;
+
+/*
+ * perf counter paranoia level:
+ *  0 - not paranoid
+ *  1 - disallow cpu counters to unpriv
+ *  2 - disallow kernel profiling to unpriv
+ */
+int sysctl_perf_counter_paranoid __read_mostly;
+
+static inline bool perf_paranoid_cpu(void)
+{
+        return sysctl_perf_counter_paranoid > 0;
+}
+
+static inline bool perf_paranoid_kernel(void)
+{
+        return sysctl_perf_counter_paranoid > 1;
+}
+
+int sysctl_perf_counter_mlock __read_mostly = 512; /* 'free' kb per user */
+
+/*
+ * max perf counter sample rate
+ */
+int sysctl_perf_counter_sample_rate __read_mostly = 100000;
+
+static atomic64_t perf_counter_id;
+
+/*
+ * Lock for (sysadmin-configurable) counter reservations:
+ */
+static DEFINE_SPINLOCK(perf_resource_lock);
+
+/*
+ * Architecture provided APIs - weak aliases:
+ */
+extern __weak const struct pmu *hw_perf_counter_init(struct perf_counter *counter)
+{
+        return NULL;
+}
+
+void __weak hw_perf_disable(void)               { barrier(); }
+void __weak hw_perf_enable(void)                { barrier(); }
+
+void __weak hw_perf_counter_setup(int cpu)      { barrier(); }
+
+int __weak
+hw_perf_group_sched_in(struct perf_counter *group_leader,
+               struct perf_cpu_context *cpuctx,
+               struct perf_counter_context *ctx, int cpu)
+{
+        return 0;
+}
+
+void __weak perf_counter_print_debug(void)      { }
+
+static DEFINE_PER_CPU(int, disable_count);
+
+void __perf_disable(void)
+{
+        __get_cpu_var(disable_count)++;
+}
+
+bool __perf_enable(void)
+{
+        return !--__get_cpu_var(disable_count);
+}
+
+void perf_disable(void)
+{
+        __perf_disable();
+        hw_perf_disable();
+}
+
+void perf_enable(void)
+{
+        if (__perf_enable())
+                hw_perf_enable();
+}
+
+static void get_ctx(struct perf_counter_context *ctx)
+{
+        atomic_inc(&ctx->refcount);
+}
+
+static void free_ctx(struct rcu_head *head)
+{
+        struct perf_counter_context *ctx;
+
+        ctx = container_of(head, struct perf_counter_context, rcu_head);
+        kfree(ctx);
+}
+
+static void put_ctx(struct perf_counter_context *ctx)
+{
+        if (atomic_dec_and_test(&ctx->refcount)) {
+                if (ctx->parent_ctx)
+                        put_ctx(ctx->parent_ctx);
+                if (ctx->task)
+                        put_task_struct(ctx->task);
+                call_rcu(&ctx->rcu_head, free_ctx);
+        }
+}
+
+/*
+ * Get the perf_counter_context for a task and lock it.
+ * This has to cope with with the fact that until it is locked,
+ * the context could get moved to another task.
+ */
+static struct perf_counter_context *
+perf_lock_task_context(struct task_struct *task, unsigned long *flags)
+{
+        struct perf_counter_context *ctx;
+
+        rcu_read_lock();
+ retry:
+        ctx = rcu_dereference(task->perf_counter_ctxp);
+        if (ctx) {
+                /*
+                 * If this context is a clone of another, it might
+                 * get swapped for another underneath us by
+                 * perf_counter_task_sched_out, though the
+                 * rcu_read_lock() protects us from any context
+                 * getting freed.  Lock the context and check if it
+                 * got swapped before we could get the lock, and retry
+                 * if so.  If we locked the right context, then it
+                 * can't get swapped on us any more.
+                 */
+                spin_lock_irqsave(&ctx->lock, *flags);
+                if (ctx != rcu_dereference(task->perf_counter_ctxp)) {
+                        spin_unlock_irqrestore(&ctx->lock, *flags);
+                        goto retry;
+                }
+        }
+        rcu_read_unlock();
+        return ctx;
+}
+
+/*
+ * Get the context for a task and increment its pin_count so it
+ * can't get swapped to another task.  This also increments its
+ * reference count so that the context can't get freed.
+ */
+static struct perf_counter_context *perf_pin_task_context(struct task_struct *task)
+{
+        struct perf_counter_context *ctx;
+        unsigned long flags;
+
+        ctx = perf_lock_task_context(task, &flags);
+        if (ctx) {
+                ++ctx->pin_count;
+                get_ctx(ctx);
+                spin_unlock_irqrestore(&ctx->lock, flags);
+        }
+        return ctx;
+}
+
+static void perf_unpin_context(struct perf_counter_context *ctx)
+{
+        unsigned long flags;
+
+        spin_lock_irqsave(&ctx->lock, flags);
+        --ctx->pin_count;
+        spin_unlock_irqrestore(&ctx->lock, flags);
+        put_ctx(ctx);
+}
+
+/*
+ * Add a counter from the lists for its context.
+ * Must be called with ctx->mutex and ctx->lock held.
+ */
+static void
+list_add_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
+{
+        struct perf_counter *group_leader = counter->group_leader;
+
+        /*
+         * Depending on whether it is a standalone or sibling counter,
+         * add it straight to the context's counter list, or to the group
+         * leader's sibling list:
+         */
+        if (group_leader == counter)
+                list_add_tail(&counter->list_entry, &ctx->counter_list);
+        else {
+                list_add_tail(&counter->list_entry, &group_leader->sibling_list);
+                group_leader->nr_siblings++;
+        }
+
+        list_add_rcu(&counter->event_entry, &ctx->event_list);
+        ctx->nr_counters++;
+}
+
+/*
+ * Remove a counter from the lists for its context.
+ * Must be called with ctx->mutex and ctx->lock held.
+ */
+static void
+list_del_counter(struct perf_counter *counter, struct perf_counter_context *ctx)
+{
+        struct perf_counter *sibling, *tmp;
+
+        if (list_empty(&counter->list_entry))
+                return;
+        ctx->nr_counters--;
+
+        list_del_init(&counter->list_entry);
+        list_del_rcu(&counter->event_entry);
+
+        if (counter->group_leader != counter)
+                counter->group_leader->nr_siblings--;
+
+        /*
+         * If this was a group counter with sibling counters then
+         * upgrade the siblings to singleton counters by adding them
+         * to the context list directly:
+         */
+        list_for_each_entry_safe(sibling, tmp,
+                                 &counter->sibling_list, list_entry) {
+
+                list_move_tail(&sibling->list_entry, &ctx->counter_list);
+                sibling->group_leader = sibling;
+        }
+}
+
+static void
+counter_sched_out(struct perf_counter *counter,
+                  struct perf_cpu_context *cpuctx,
+                  struct perf_counter_context *ctx)
+{
+        if (counter->state != PERF_COUNTER_STATE_ACTIVE)
+                return;
+
+        counter->state = PERF_COUNTER_STATE_INACTIVE;
+        counter->tstamp_stopped = ctx->time;
+        counter->pmu->disable(counter);
+        counter->oncpu = -1;
+
+        if (!is_software_counter(counter))
+                cpuctx->active_oncpu--;
+        ctx->nr_active--;
+        if (counter->attr.exclusive || !cpuctx->active_oncpu)
+                cpuctx->exclusive = 0;
+}
+
+static void
+group_sched_out(struct perf_counter *group_counter,
+                struct perf_cpu_context *cpuctx,
+                struct perf_counter_context *ctx)
+{
+        struct perf_counter *counter;
+
+        if (group_counter->state != PERF_COUNTER_STATE_ACTIVE)
+                return;
+
+        counter_sched_out(group_counter, cpuctx, ctx);
+
+        /*
+         * Schedule out siblings (if any):
+         */
+        list_for_each_entry(counter, &group_counter->sibling_list, list_entry)
+                counter_sched_out(counter, cpuctx, ctx);
+
+        if (group_counter->attr.exclusive)
+                cpuctx->exclusive = 0;
+}
+
+/*
+ * Cross CPU call to remove a performance counter
+ *
+ * We disable the counter on the hardware level first. After that we
+ * remove it from the context list.
+ */
+static void __perf_counter_remove_from_context(void *info)
+{
+        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+        struct perf_counter *counter = info;
+        struct perf_counter_context *ctx = counter->ctx;
+
+        /*
+         * If this is a task context, we need to check whether it is
+         * the current task context of this cpu. If not it has been
+         * scheduled out before the smp call arrived.
+         */
+        if (ctx->task && cpuctx->task_ctx != ctx)
+                return;
+
+        spin_lock(&ctx->lock);
+        /*
+         * Protect the list operation against NMI by disabling the
+         * counters on a global level.
+         */
+        perf_disable();
+
+        counter_sched_out(counter, cpuctx, ctx);
+
+        list_del_counter(counter, ctx);
+
+        if (!ctx->task) {
+                /*
+                 * Allow more per task counters with respect to the
+                 * reservation:
+                 */
+                cpuctx->max_pertask =
+                        min(perf_max_counters - ctx->nr_counters,
+                            perf_max_counters - perf_reserved_percpu);
+        }
+
+        perf_enable();
+        spin_unlock(&ctx->lock);
+}
+
+
+/*
+ * Remove the counter from a task's (or a CPU's) list of counters.
+ *
+ * Must be called with ctx->mutex held.
+ *
+ * CPU counters are removed with a smp call. For task counters we only
+ * call when the task is on a CPU.
+ *
+ * If counter->ctx is a cloned context, callers must make sure that
+ * every task struct that counter->ctx->task could possibly point to
+ * remains valid.  This is OK when called from perf_release since
+ * that only calls us on the top-level context, which can't be a clone.
+ * When called from perf_counter_exit_task, it's OK because the
+ * context has been detached from its task.
+ */
+static void perf_counter_remove_from_context(struct perf_counter *counter)
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        struct task_struct *task = ctx->task;
+
+        if (!task) {
+                /*
+                 * Per cpu counters are removed via an smp call and
+                 * the removal is always sucessful.
+                 */
+                smp_call_function_single(counter->cpu,
+                                         __perf_counter_remove_from_context,
+                                         counter, 1);
+                return;
+        }
+
+retry:
+        task_oncpu_function_call(task, __perf_counter_remove_from_context,
+                                 counter);
+
+        spin_lock_irq(&ctx->lock);
+        /*
+         * If the context is active we need to retry the smp call.
+         */
+        if (ctx->nr_active && !list_empty(&counter->list_entry)) {
+                spin_unlock_irq(&ctx->lock);
+                goto retry;
+        }
+
+        /*
+         * The lock prevents that this context is scheduled in so we
+         * can remove the counter safely, if the call above did not
+         * succeed.
+         */
+        if (!list_empty(&counter->list_entry)) {
+                list_del_counter(counter, ctx);
+        }
+        spin_unlock_irq(&ctx->lock);
+}
+
+static inline u64 perf_clock(void)
+{
+        return cpu_clock(smp_processor_id());
+}
+
+/*
+ * Update the record of the current time in a context.
+ */
+static void update_context_time(struct perf_counter_context *ctx)
+{
+        u64 now = perf_clock();
+
+        ctx->time += now - ctx->timestamp;
+        ctx->timestamp = now;
+}
+
+/*
+ * Update the total_time_enabled and total_time_running fields for a counter.
+ */
+static void update_counter_times(struct perf_counter *counter)
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        u64 run_end;
+
+        if (counter->state < PERF_COUNTER_STATE_INACTIVE)
+                return;
+
+        counter->total_time_enabled = ctx->time - counter->tstamp_enabled;
+
+        if (counter->state == PERF_COUNTER_STATE_INACTIVE)
+                run_end = counter->tstamp_stopped;
+        else
+                run_end = ctx->time;
+
+        counter->total_time_running = run_end - counter->tstamp_running;
+}
+
+/*
+ * Update total_time_enabled and total_time_running for all counters in a group.
+ */
+static void update_group_times(struct perf_counter *leader)
+{
+        struct perf_counter *counter;
+
+        update_counter_times(leader);
+        list_for_each_entry(counter, &leader->sibling_list, list_entry)
+                update_counter_times(counter);
+}
+
+/*
+ * Cross CPU call to disable a performance counter
+ */
+static void __perf_counter_disable(void *info)
+{
+        struct perf_counter *counter = info;
+        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+        struct perf_counter_context *ctx = counter->ctx;
+
+        /*
+         * If this is a per-task counter, need to check whether this
+         * counter's task is the current task on this cpu.
+         */
+        if (ctx->task && cpuctx->task_ctx != ctx)
+                return;
+
+        spin_lock(&ctx->lock);
+
+        /*
+         * If the counter is on, turn it off.
+         * If it is in error state, leave it in error state.
+         */
+        if (counter->state >= PERF_COUNTER_STATE_INACTIVE) {
+                update_context_time(ctx);
+                update_counter_times(counter);
+                if (counter == counter->group_leader)
+                        group_sched_out(counter, cpuctx, ctx);
+                else
+                        counter_sched_out(counter, cpuctx, ctx);
+                counter->state = PERF_COUNTER_STATE_OFF;
+        }
+
+        spin_unlock(&ctx->lock);
+}
+
+/*
+ * Disable a counter.
+ *
+ * If counter->ctx is a cloned context, callers must make sure that
+ * every task struct that counter->ctx->task could possibly point to
+ * remains valid.  This condition is satisifed when called through
+ * perf_counter_for_each_child or perf_counter_for_each because they
+ * hold the top-level counter's child_mutex, so any descendant that
+ * goes to exit will block in sync_child_counter.
+ * When called from perf_pending_counter it's OK because counter->ctx
+ * is the current context on this CPU and preemption is disabled,
+ * hence we can't get into perf_counter_task_sched_out for this context.
+ */
+static void perf_counter_disable(struct perf_counter *counter)
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        struct task_struct *task = ctx->task;
+
+        if (!task) {
+                /*
+                 * Disable the counter on the cpu that it's on
+                 */
+                smp_call_function_single(counter->cpu, __perf_counter_disable,
+                                         counter, 1);
+                return;
+        }
+
+ retry:
+        task_oncpu_function_call(task, __perf_counter_disable, counter);
+
+        spin_lock_irq(&ctx->lock);
+        /*
+         * If the counter is still active, we need to retry the cross-call.
+         */
+        if (counter->state == PERF_COUNTER_STATE_ACTIVE) {
+                spin_unlock_irq(&ctx->lock);
+                goto retry;
+        }
+
+        /*
+         * Since we have the lock this context can't be scheduled
+         * in, so we can change the state safely.
+         */
+        if (counter->state == PERF_COUNTER_STATE_INACTIVE) {
+                update_counter_times(counter);
+                counter->state = PERF_COUNTER_STATE_OFF;
+        }
+
+        spin_unlock_irq(&ctx->lock);
+}
+
+static int
+counter_sched_in(struct perf_counter *counter,
+                 struct perf_cpu_context *cpuctx,
+                 struct perf_counter_context *ctx,
+                 int cpu)
+{
+        if (counter->state <= PERF_COUNTER_STATE_OFF)
+                return 0;
+
+        counter->state = PERF_COUNTER_STATE_ACTIVE;
+        counter->oncpu = cpu;   /* TODO: put 'cpu' into cpuctx->cpu */
+        /*
+         * The new state must be visible before we turn it on in the hardware:
+         */
+        smp_wmb();
+
+        if (counter->pmu->enable(counter)) {
+                counter->state = PERF_COUNTER_STATE_INACTIVE;
+                counter->oncpu = -1;
+                return -EAGAIN;
+        }
+
+        counter->tstamp_running += ctx->time - counter->tstamp_stopped;
+
+        if (!is_software_counter(counter))
+                cpuctx->active_oncpu++;
+        ctx->nr_active++;
+
+        if (counter->attr.exclusive)
+                cpuctx->exclusive = 1;
+
+        return 0;
+}
+
+static int
+group_sched_in(struct perf_counter *group_counter,
+               struct perf_cpu_context *cpuctx,
+               struct perf_counter_context *ctx,
+               int cpu)
+{
+        struct perf_counter *counter, *partial_group;
+        int ret;
+
+        if (group_counter->state == PERF_COUNTER_STATE_OFF)
+                return 0;
+
+        ret = hw_perf_group_sched_in(group_counter, cpuctx, ctx, cpu);
+        if (ret)
+                return ret < 0 ? ret : 0;
+
+        if (counter_sched_in(group_counter, cpuctx, ctx, cpu))
+                return -EAGAIN;
+
+        /*
+         * Schedule in siblings as one group (if any):
+         */
+        list_for_each_entry(counter, &group_counter->sibling_list, list_entry) {
+                if (counter_sched_in(counter, cpuctx, ctx, cpu)) {
+                        partial_group = counter;
+                        goto group_error;
+                }
+        }
+
+        return 0;
+
+group_error:
+        /*
+         * Groups can be scheduled in as one unit only, so undo any
+         * partial group before returning:
+         */
+        list_for_each_entry(counter, &group_counter->sibling_list, list_entry) {
+                if (counter == partial_group)
+                        break;
+                counter_sched_out(counter, cpuctx, ctx);
+        }
+        counter_sched_out(group_counter, cpuctx, ctx);
+
+        return -EAGAIN;
+}
+
+/*
+ * Return 1 for a group consisting entirely of software counters,
+ * 0 if the group contains any hardware counters.
+ */
+static int is_software_only_group(struct perf_counter *leader)
+{
+        struct perf_counter *counter;
+
+        if (!is_software_counter(leader))
+                return 0;
+
+        list_for_each_entry(counter, &leader->sibling_list, list_entry)
+                if (!is_software_counter(counter))
+                        return 0;
+
+        return 1;
+}
+
+/*
+ * Work out whether we can put this counter group on the CPU now.
+ */
+static int group_can_go_on(struct perf_counter *counter,
+                           struct perf_cpu_context *cpuctx,
+                           int can_add_hw)
+{
+        /*
+         * Groups consisting entirely of software counters can always go on.
+         */
+        if (is_software_only_group(counter))
+                return 1;
+        /*
+         * If an exclusive group is already on, no other hardware
+         * counters can go on.
+         */
+        if (cpuctx->exclusive)
+                return 0;
+        /*
+         * If this group is exclusive and there are already
+         * counters on the CPU, it can't go on.
+         */
+        if (counter->attr.exclusive && cpuctx->active_oncpu)
+                return 0;
+        /*
+         * Otherwise, try to add it if all previous groups were able
+         * to go on.
+         */
+        return can_add_hw;
+}
+
+static void add_counter_to_ctx(struct perf_counter *counter,
+                               struct perf_counter_context *ctx)
+{
+        list_add_counter(counter, ctx);
+        counter->tstamp_enabled = ctx->time;
+        counter->tstamp_running = ctx->time;
+        counter->tstamp_stopped = ctx->time;
+}
+
+/*
+ * Cross CPU call to install and enable a performance counter
+ *
+ * Must be called with ctx->mutex held
+ */
+static void __perf_install_in_context(void *info)
+{
+        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+        struct perf_counter *counter = info;
+        struct perf_counter_context *ctx = counter->ctx;
+        struct perf_counter *leader = counter->group_leader;
+        int cpu = smp_processor_id();
+        int err;
+
+        /*
+         * If this is a task context, we need to check whether it is
+         * the current task context of this cpu. If not it has been
+         * scheduled out before the smp call arrived.
+         * Or possibly this is the right context but it isn't
+         * on this cpu because it had no counters.
+         */
+        if (ctx->task && cpuctx->task_ctx != ctx) {
+                if (cpuctx->task_ctx || ctx->task != current)
+                        return;
+                cpuctx->task_ctx = ctx;
+        }
+
+        spin_lock(&ctx->lock);
+        ctx->is_active = 1;
+        update_context_time(ctx);
+
+        /*
+         * Protect the list operation against NMI by disabling the
+         * counters on a global level. NOP for non NMI based counters.
+         */
+        perf_disable();
+
+        add_counter_to_ctx(counter, ctx);
+
+        /*
+         * Don't put the counter on if it is disabled or if
+         * it is in a group and the group isn't on.
+         */
+        if (counter->state != PERF_COUNTER_STATE_INACTIVE ||
+            (leader != counter && leader->state != PERF_COUNTER_STATE_ACTIVE))
+                goto unlock;
+
+        /*
+         * An exclusive counter can't go on if there are already active
+         * hardware counters, and no hardware counter can go on if there
+         * is already an exclusive counter on.
+         */
+        if (!group_can_go_on(counter, cpuctx, 1))
+                err = -EEXIST;
+        else
+                err = counter_sched_in(counter, cpuctx, ctx, cpu);
+
+        if (err) {
+                /*
+                 * This counter couldn't go on.  If it is in a group
+                 * then we have to pull the whole group off.
+                 * If the counter group is pinned then put it in error state.
+                 */
+                if (leader != counter)
+                        group_sched_out(leader, cpuctx, ctx);
+                if (leader->attr.pinned) {
+                        update_group_times(leader);
+                        leader->state = PERF_COUNTER_STATE_ERROR;
+                }
+        }
+
+        if (!err && !ctx->task && cpuctx->max_pertask)
+                cpuctx->max_pertask--;
+
+ unlock:
+        perf_enable();
+
+        spin_unlock(&ctx->lock);
+}
+
+/*
+ * Attach a performance counter to a context
+ *
+ * First we add the counter to the list with the hardware enable bit
+ * in counter->hw_config cleared.
+ *
+ * If the counter is attached to a task which is on a CPU we use a smp
+ * call to enable it in the task context. The task might have been
+ * scheduled away, but we check this in the smp call again.
+ *
+ * Must be called with ctx->mutex held.
+ */
+static void
+perf_install_in_context(struct perf_counter_context *ctx,
+                        struct perf_counter *counter,
+                        int cpu)
+{
+        struct task_struct *task = ctx->task;
+
+        if (!task) {
+                /*
+                 * Per cpu counters are installed via an smp call and
+                 * the install is always sucessful.
+                 */
+                smp_call_function_single(cpu, __perf_install_in_context,
+                                         counter, 1);
+                return;
+        }
+
+retry:
+        task_oncpu_function_call(task, __perf_install_in_context,
+                                 counter);
+
+        spin_lock_irq(&ctx->lock);
+        /*
+         * we need to retry the smp call.
+         */
+        if (ctx->is_active && list_empty(&counter->list_entry)) {
+                spin_unlock_irq(&ctx->lock);
+                goto retry;
+        }
+
+        /*
+         * The lock prevents that this context is scheduled in so we
+         * can add the counter safely, if it the call above did not
+         * succeed.
+         */
+        if (list_empty(&counter->list_entry))
+                add_counter_to_ctx(counter, ctx);
+        spin_unlock_irq(&ctx->lock);
+}
+
+/*
+ * Cross CPU call to enable a performance counter
+ */
+static void __perf_counter_enable(void *info)
+{
+        struct perf_counter *counter = info;
+        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+        struct perf_counter_context *ctx = counter->ctx;
+        struct perf_counter *leader = counter->group_leader;
+        int err;
+
+        /*
+         * If this is a per-task counter, need to check whether this
+         * counter's task is the current task on this cpu.
+         */
+        if (ctx->task && cpuctx->task_ctx != ctx) {
+                if (cpuctx->task_ctx || ctx->task != current)
+                        return;
+                cpuctx->task_ctx = ctx;
+        }
+
+        spin_lock(&ctx->lock);
+        ctx->is_active = 1;
+        update_context_time(ctx);
+
+        if (counter->state >= PERF_COUNTER_STATE_INACTIVE)
+                goto unlock;
+        counter->state = PERF_COUNTER_STATE_INACTIVE;
+        counter->tstamp_enabled = ctx->time - counter->total_time_enabled;
+
+        /*
+         * If the counter is in a group and isn't the group leader,
+         * then don't put it on unless the group is on.
+         */
+        if (leader != counter && leader->state != PERF_COUNTER_STATE_ACTIVE)
+                goto unlock;
+
+        if (!group_can_go_on(counter, cpuctx, 1)) {
+                err = -EEXIST;
+        } else {
+                perf_disable();
+                if (counter == leader)
+                        err = group_sched_in(counter, cpuctx, ctx,
+                                             smp_processor_id());
+                else
+                        err = counter_sched_in(counter, cpuctx, ctx,
+                                               smp_processor_id());
+                perf_enable();
+        }
+
+        if (err) {
+                /*
+                 * If this counter can't go on and it's part of a
+                 * group, then the whole group has to come off.
+                 */
+                if (leader != counter)
+                        group_sched_out(leader, cpuctx, ctx);
+                if (leader->attr.pinned) {
+                        update_group_times(leader);
+                        leader->state = PERF_COUNTER_STATE_ERROR;
+                }
+        }
+
+ unlock:
+        spin_unlock(&ctx->lock);
+}
+
+/*
+ * Enable a counter.
+ *
+ * If counter->ctx is a cloned context, callers must make sure that
+ * every task struct that counter->ctx->task could possibly point to
+ * remains valid.  This condition is satisfied when called through
+ * perf_counter_for_each_child or perf_counter_for_each as described
+ * for perf_counter_disable.
+ */
+static void perf_counter_enable(struct perf_counter *counter)
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        struct task_struct *task = ctx->task;
+
+        if (!task) {
+                /*
+                 * Enable the counter on the cpu that it's on
+                 */
+                smp_call_function_single(counter->cpu, __perf_counter_enable,
+                                         counter, 1);
+                return;
+        }
+
+        spin_lock_irq(&ctx->lock);
+        if (counter->state >= PERF_COUNTER_STATE_INACTIVE)
+                goto out;
+
+        /*
+         * If the counter is in error state, clear that first.
+         * That way, if we see the counter in error state below, we
+         * know that it has gone back into error state, as distinct
+         * from the task having been scheduled away before the
+         * cross-call arrived.
+         */
+        if (counter->state == PERF_COUNTER_STATE_ERROR)
+                counter->state = PERF_COUNTER_STATE_OFF;
+
+ retry:
+        spin_unlock_irq(&ctx->lock);
+        task_oncpu_function_call(task, __perf_counter_enable, counter);
+
+        spin_lock_irq(&ctx->lock);
+
+        /*
+         * If the context is active and the counter is still off,
+         * we need to retry the cross-call.
+         */
+        if (ctx->is_active && counter->state == PERF_COUNTER_STATE_OFF)
+                goto retry;
+
+        /*
+         * Since we have the lock this context can't be scheduled
+         * in, so we can change the state safely.
+         */
+        if (counter->state == PERF_COUNTER_STATE_OFF) {
+                counter->state = PERF_COUNTER_STATE_INACTIVE;
+                counter->tstamp_enabled =
+                        ctx->time - counter->total_time_enabled;
+        }
+ out:
+        spin_unlock_irq(&ctx->lock);
+}
+
+static int perf_counter_refresh(struct perf_counter *counter, int refresh)
+{
+        /*
+         * not supported on inherited counters
+         */
+        if (counter->attr.inherit)
+                return -EINVAL;
+
+        atomic_add(refresh, &counter->event_limit);
+        perf_counter_enable(counter);
+
+        return 0;
+}
+
+void __perf_counter_sched_out(struct perf_counter_context *ctx,
+                              struct perf_cpu_context *cpuctx)
+{
+        struct perf_counter *counter;
+
+        spin_lock(&ctx->lock);
+        ctx->is_active = 0;
+        if (likely(!ctx->nr_counters))
+                goto out;
+        update_context_time(ctx);
+
+        perf_disable();
+        if (ctx->nr_active) {
+                list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                        if (counter != counter->group_leader)
+                                counter_sched_out(counter, cpuctx, ctx);
+                        else
+                                group_sched_out(counter, cpuctx, ctx);
+                }
+        }
+        perf_enable();
+ out:
+        spin_unlock(&ctx->lock);
+}
+
+/*
+ * Test whether two contexts are equivalent, i.e. whether they
+ * have both been cloned from the same version of the same context
+ * and they both have the same number of enabled counters.
+ * If the number of enabled counters is the same, then the set
+ * of enabled counters should be the same, because these are both
+ * inherited contexts, therefore we can't access individual counters
+ * in them directly with an fd; we can only enable/disable all
+ * counters via prctl, or enable/disable all counters in a family
+ * via ioctl, which will have the same effect on both contexts.
+ */
+static int context_equiv(struct perf_counter_context *ctx1,
+                         struct perf_counter_context *ctx2)
+{
+        return ctx1->parent_ctx && ctx1->parent_ctx == ctx2->parent_ctx
+                && ctx1->parent_gen == ctx2->parent_gen
+                && !ctx1->pin_count && !ctx2->pin_count;
+}
+
+/*
+ * Called from scheduler to remove the counters of the current task,
+ * with interrupts disabled.
+ *
+ * We stop each counter and update the counter value in counter->count.
+ *
+ * This does not protect us against NMI, but disable()
+ * sets the disabled bit in the control field of counter _before_
+ * accessing the counter control register. If a NMI hits, then it will
+ * not restart the counter.
+ */
+void perf_counter_task_sched_out(struct task_struct *task,
+                                 struct task_struct *next, int cpu)
+{
+        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
+        struct perf_counter_context *ctx = task->perf_counter_ctxp;
+        struct perf_counter_context *next_ctx;
+        struct perf_counter_context *parent;
+        struct pt_regs *regs;
+        int do_switch = 1;
+
+        regs = task_pt_regs(task);
+        perf_swcounter_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 1, regs, 0);
+
+        if (likely(!ctx || !cpuctx->task_ctx))
+                return;
+
+        update_context_time(ctx);
+
+        rcu_read_lock();
+        parent = rcu_dereference(ctx->parent_ctx);
+        next_ctx = next->perf_counter_ctxp;
+        if (parent && next_ctx &&
+            rcu_dereference(next_ctx->parent_ctx) == parent) {
+                /*
+                 * Looks like the two contexts are clones, so we might be
+                 * able to optimize the context switch.  We lock both
+                 * contexts and check that they are clones under the
+                 * lock (including re-checking that neither has been
+                 * uncloned in the meantime).  It doesn't matter which
+                 * order we take the locks because no other cpu could
+                 * be trying to lock both of these tasks.
+                 */
+                spin_lock(&ctx->lock);
+                spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
+                if (context_equiv(ctx, next_ctx)) {
+                        /*
+                         * XXX do we need a memory barrier of sorts
+                         * wrt to rcu_dereference() of perf_counter_ctxp
+                         */
+                        task->perf_counter_ctxp = next_ctx;
+                        next->perf_counter_ctxp = ctx;
+                        ctx->task = next;
+                        next_ctx->task = task;
+                        do_switch = 0;
+                }
+                spin_unlock(&next_ctx->lock);
+                spin_unlock(&ctx->lock);
+        }
+        rcu_read_unlock();
+
+        if (do_switch) {
+                __perf_counter_sched_out(ctx, cpuctx);
+                cpuctx->task_ctx = NULL;
+        }
+}
+
+/*
+ * Called with IRQs disabled
+ */
+static void __perf_counter_task_sched_out(struct perf_counter_context *ctx)
+{
+        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+
+        if (!cpuctx->task_ctx)
+                return;
+
+        if (WARN_ON_ONCE(ctx != cpuctx->task_ctx))
+                return;
+
+        __perf_counter_sched_out(ctx, cpuctx);
+        cpuctx->task_ctx = NULL;
+}
+
+/*
+ * Called with IRQs disabled
+ */
+static void perf_counter_cpu_sched_out(struct perf_cpu_context *cpuctx)
+{
+        __perf_counter_sched_out(&cpuctx->ctx, cpuctx);
+}
+
+static void
+__perf_counter_sched_in(struct perf_counter_context *ctx,
+                        struct perf_cpu_context *cpuctx, int cpu)
+{
+        struct perf_counter *counter;
+        int can_add_hw = 1;
+
+        spin_lock(&ctx->lock);
+        ctx->is_active = 1;
+        if (likely(!ctx->nr_counters))
+                goto out;
+
+        ctx->timestamp = perf_clock();
+
+        perf_disable();
+
+        /*
+         * First go through the list and put on any pinned groups
+         * in order to give them the best chance of going on.
+         */
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                if (counter->state <= PERF_COUNTER_STATE_OFF ||
+                    !counter->attr.pinned)
+                        continue;
+                if (counter->cpu != -1 && counter->cpu != cpu)
+                        continue;
+
+                if (counter != counter->group_leader)
+                        counter_sched_in(counter, cpuctx, ctx, cpu);
+                else {
+                        if (group_can_go_on(counter, cpuctx, 1))
+                                group_sched_in(counter, cpuctx, ctx, cpu);
+                }
+
+                /*
+                 * If this pinned group hasn't been scheduled,
+                 * put it in error state.
+                 */
+                if (counter->state == PERF_COUNTER_STATE_INACTIVE) {
+                        update_group_times(counter);
+                        counter->state = PERF_COUNTER_STATE_ERROR;
+                }
+        }
+
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                /*
+                 * Ignore counters in OFF or ERROR state, and
+                 * ignore pinned counters since we did them already.
+                 */
+                if (counter->state <= PERF_COUNTER_STATE_OFF ||
+                    counter->attr.pinned)
+                        continue;
+
+                /*
+                 * Listen to the 'cpu' scheduling filter constraint
+                 * of counters:
+                 */
+                if (counter->cpu != -1 && counter->cpu != cpu)
+                        continue;
+
+                if (counter != counter->group_leader) {
+                        if (counter_sched_in(counter, cpuctx, ctx, cpu))
+                                can_add_hw = 0;
+                } else {
+                        if (group_can_go_on(counter, cpuctx, can_add_hw)) {
+                                if (group_sched_in(counter, cpuctx, ctx, cpu))
+                                        can_add_hw = 0;
+                        }
+                }
+        }
+        perf_enable();
+ out:
+        spin_unlock(&ctx->lock);
+}
+
+/*
+ * Called from scheduler to add the counters of the current task
+ * with interrupts disabled.
+ *
+ * We restore the counter value and then enable it.
+ *
+ * This does not protect us against NMI, but enable()
+ * sets the enabled bit in the control field of counter _before_
+ * accessing the counter control register. If a NMI hits, then it will
+ * keep the counter running.
+ */
+void perf_counter_task_sched_in(struct task_struct *task, int cpu)
+{
+        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
+        struct perf_counter_context *ctx = task->perf_counter_ctxp;
+
+        if (likely(!ctx))
+                return;
+        if (cpuctx->task_ctx == ctx)
+                return;
+        __perf_counter_sched_in(ctx, cpuctx, cpu);
+        cpuctx->task_ctx = ctx;
+}
+
+static void perf_counter_cpu_sched_in(struct perf_cpu_context *cpuctx, int cpu)
+{
+        struct perf_counter_context *ctx = &cpuctx->ctx;
+
+        __perf_counter_sched_in(ctx, cpuctx, cpu);
+}
+
+#define MAX_INTERRUPTS (~0ULL)
+
+static void perf_log_throttle(struct perf_counter *counter, int enable);
+static void perf_log_period(struct perf_counter *counter, u64 period);
+
+static void perf_adjust_period(struct perf_counter *counter, u64 events)
+{
+        struct hw_perf_counter *hwc = &counter->hw;
+        u64 period, sample_period;
+        s64 delta;
+
+        events *= hwc->sample_period;
+        period = div64_u64(events, counter->attr.sample_freq);
+
+        delta = (s64)(period - hwc->sample_period);
+        delta = (delta + 7) / 8; /* low pass filter */
+
+        sample_period = hwc->sample_period + delta;
+
+        if (!sample_period)
+                sample_period = 1;
+
+        perf_log_period(counter, sample_period);
+
+        hwc->sample_period = sample_period;
+}
+
+static void perf_ctx_adjust_freq(struct perf_counter_context *ctx)
+{
+        struct perf_counter *counter;
+        struct hw_perf_counter *hwc;
+        u64 interrupts, freq;
+
+        spin_lock(&ctx->lock);
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                if (counter->state != PERF_COUNTER_STATE_ACTIVE)
+                        continue;
+
+                hwc = &counter->hw;
+
+                interrupts = hwc->interrupts;
+                hwc->interrupts = 0;
+
+                /*
+                 * unthrottle counters on the tick
+                 */
+                if (interrupts == MAX_INTERRUPTS) {
+                        perf_log_throttle(counter, 1);
+                        counter->pmu->unthrottle(counter);
+                        interrupts = 2*sysctl_perf_counter_sample_rate/HZ;
+                }
+
+                if (!counter->attr.freq || !counter->attr.sample_freq)
+                        continue;
+
+                /*
+                 * if the specified freq < HZ then we need to skip ticks
+                 */
+                if (counter->attr.sample_freq < HZ) {
+                        freq = counter->attr.sample_freq;
+
+                        hwc->freq_count += freq;
+                        hwc->freq_interrupts += interrupts;
+
+                        if (hwc->freq_count < HZ)
+                                continue;
+
+                        interrupts = hwc->freq_interrupts;
+                        hwc->freq_interrupts = 0;
+                        hwc->freq_count -= HZ;
+                } else
+                        freq = HZ;
+
+                perf_adjust_period(counter, freq * interrupts);
+
+                /*
+                 * In order to avoid being stalled by an (accidental) huge
+                 * sample period, force reset the sample period if we didn't
+                 * get any events in this freq period.
+                 */
+                if (!interrupts) {
+                        perf_disable();
+                        counter->pmu->disable(counter);
+                        atomic_set(&hwc->period_left, 0);
+                        counter->pmu->enable(counter);
+                        perf_enable();
+                }
+        }
+        spin_unlock(&ctx->lock);
+}
+
+/*
+ * Round-robin a context's counters:
+ */
+static void rotate_ctx(struct perf_counter_context *ctx)
+{
+        struct perf_counter *counter;
+
+        if (!ctx->nr_counters)
+                return;
+
+        spin_lock(&ctx->lock);
+        /*
+         * Rotate the first entry last (works just fine for group counters too):
+         */
+        perf_disable();
+        list_for_each_entry(counter, &ctx->counter_list, list_entry) {
+                list_move_tail(&counter->list_entry, &ctx->counter_list);
+                break;
+        }
+        perf_enable();
+
+        spin_unlock(&ctx->lock);
+}
+
+void perf_counter_task_tick(struct task_struct *curr, int cpu)
+{
+        struct perf_cpu_context *cpuctx;
+        struct perf_counter_context *ctx;
+
+        if (!atomic_read(&nr_counters))
+                return;
+
+        cpuctx = &per_cpu(perf_cpu_context, cpu);
+        ctx = curr->perf_counter_ctxp;
+
+        perf_ctx_adjust_freq(&cpuctx->ctx);
+        if (ctx)
+                perf_ctx_adjust_freq(ctx);
+
+        perf_counter_cpu_sched_out(cpuctx);
+        if (ctx)
+                __perf_counter_task_sched_out(ctx);
+
+        rotate_ctx(&cpuctx->ctx);
+        if (ctx)
+                rotate_ctx(ctx);
+
+        perf_counter_cpu_sched_in(cpuctx, cpu);
+        if (ctx)
+                perf_counter_task_sched_in(curr, cpu);
+}
+
+/*
+ * Cross CPU call to read the hardware counter
+ */
+static void __read(void *info)
+{
+        struct perf_counter *counter = info;
+        struct perf_counter_context *ctx = counter->ctx;
+        unsigned long flags;
+
+        local_irq_save(flags);
+        if (ctx->is_active)
+                update_context_time(ctx);
+        counter->pmu->read(counter);
+        update_counter_times(counter);
+        local_irq_restore(flags);
+}
+
+static u64 perf_counter_read(struct perf_counter *counter)
+{
+        /*
+         * If counter is enabled and currently active on a CPU, update the
+         * value in the counter structure:
+         */
+        if (counter->state == PERF_COUNTER_STATE_ACTIVE) {
+                smp_call_function_single(counter->oncpu,
+                                         __read, counter, 1);
+        } else if (counter->state == PERF_COUNTER_STATE_INACTIVE) {
+                update_counter_times(counter);
+        }
+
+        return atomic64_read(&counter->count);
+}
+
+/*
+ * Initialize the perf_counter context in a task_struct:
+ */
+static void
+__perf_counter_init_context(struct perf_counter_context *ctx,
+                            struct task_struct *task)
+{
+        memset(ctx, 0, sizeof(*ctx));
+        spin_lock_init(&ctx->lock);
+        mutex_init(&ctx->mutex);
+        INIT_LIST_HEAD(&ctx->counter_list);
+        INIT_LIST_HEAD(&ctx->event_list);
+        atomic_set(&ctx->refcount, 1);
+        ctx->task = task;
+}
+
+static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
+{
+        struct perf_counter_context *parent_ctx;
+        struct perf_counter_context *ctx;
+        struct perf_cpu_context *cpuctx;
+        struct task_struct *task;
+        unsigned long flags;
+        int err;
+
+        /*
+         * If cpu is not a wildcard then this is a percpu counter:
+         */
+        if (cpu != -1) {
+                /* Must be root to operate on a CPU counter: */
+                if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
+                        return ERR_PTR(-EACCES);
+
+                if (cpu < 0 || cpu > num_possible_cpus())
+                        return ERR_PTR(-EINVAL);
+
+                /*
+                 * We could be clever and allow to attach a counter to an
+                 * offline CPU and activate it when the CPU comes up, but
+                 * that's for later.
+                 */
+                if (!cpu_isset(cpu, cpu_online_map))
+                        return ERR_PTR(-ENODEV);
+
+                cpuctx = &per_cpu(perf_cpu_context, cpu);
+                ctx = &cpuctx->ctx;
+                get_ctx(ctx);
+
+                return ctx;
+        }
+
+        rcu_read_lock();
+        if (!pid)
+                task = current;
+        else
+                task = find_task_by_vpid(pid);
+        if (task)
+                get_task_struct(task);
+        rcu_read_unlock();
+
+        if (!task)
+                return ERR_PTR(-ESRCH);
+
+        /*
+         * Can't attach counters to a dying task.
+         */
+        err = -ESRCH;
+        if (task->flags & PF_EXITING)
+                goto errout;
+
+        /* Reuse ptrace permission checks for now. */
+        err = -EACCES;
+        if (!ptrace_may_access(task, PTRACE_MODE_READ))
+                goto errout;
+
+ retry:
+        ctx = perf_lock_task_context(task, &flags);
+        if (ctx) {
+                parent_ctx = ctx->parent_ctx;
+                if (parent_ctx) {
+                        put_ctx(parent_ctx);
+                        ctx->parent_ctx = NULL;         /* no longer a clone */
+                }
+                /*
+                 * Get an extra reference before dropping the lock so that
+                 * this context won't get freed if the task exits.
+                 */
+                get_ctx(ctx);
+                spin_unlock_irqrestore(&ctx->lock, flags);
+        }
+
+        if (!ctx) {
+                ctx = kmalloc(sizeof(struct perf_counter_context), GFP_KERNEL);
+                err = -ENOMEM;
+                if (!ctx)
+                        goto errout;
+                __perf_counter_init_context(ctx, task);
+                get_ctx(ctx);
+                if (cmpxchg(&task->perf_counter_ctxp, NULL, ctx)) {
+                        /*
+                         * We raced with some other task; use
+                         * the context they set.
+                         */
+                        kfree(ctx);
+                        goto retry;
+                }
+                get_task_struct(task);
+        }
+
+        put_task_struct(task);
+        return ctx;
+
+ errout:
+        put_task_struct(task);
+        return ERR_PTR(err);
+}
+
+static void free_counter_rcu(struct rcu_head *head)
+{
+        struct perf_counter *counter;
+
+        counter = container_of(head, struct perf_counter, rcu_head);
+        if (counter->ns)
+                put_pid_ns(counter->ns);
+        kfree(counter);
+}
+
+static void perf_pending_sync(struct perf_counter *counter);
+
+static void free_counter(struct perf_counter *counter)
+{
+        perf_pending_sync(counter);
+
+        atomic_dec(&nr_counters);
+        if (counter->attr.mmap)
+                atomic_dec(&nr_mmap_counters);
+        if (counter->attr.comm)
+                atomic_dec(&nr_comm_counters);
+
+        if (counter->destroy)
+                counter->destroy(counter);
+
+        put_ctx(counter->ctx);
+        call_rcu(&counter->rcu_head, free_counter_rcu);
+}
+
+/*
+ * Called when the last reference to the file is gone.
+ */
+static int perf_release(struct inode *inode, struct file *file)
+{
+        struct perf_counter *counter = file->private_data;
+        struct perf_counter_context *ctx = counter->ctx;
+
+        file->private_data = NULL;
+
+        WARN_ON_ONCE(ctx->parent_ctx);
+        mutex_lock(&ctx->mutex);
+        perf_counter_remove_from_context(counter);
+        mutex_unlock(&ctx->mutex);
+
+        mutex_lock(&counter->owner->perf_counter_mutex);
+        list_del_init(&counter->owner_entry);
+        mutex_unlock(&counter->owner->perf_counter_mutex);
+        put_task_struct(counter->owner);
+
+        free_counter(counter);
+
+        return 0;
+}
+
+/*
+ * Read the performance counter - simple non blocking version for now
+ */
+static ssize_t
+perf_read_hw(struct perf_counter *counter, char __user *buf, size_t count)
+{
+        u64 values[3];
+        int n;
+
+        /*
+         * Return end-of-file for a read on a counter that is in
+         * error state (i.e. because it was pinned but it couldn't be
+         * scheduled on to the CPU at some point).
+         */
+        if (counter->state == PERF_COUNTER_STATE_ERROR)
+                return 0;
+
+        WARN_ON_ONCE(counter->ctx->parent_ctx);
+        mutex_lock(&counter->child_mutex);
+        values[0] = perf_counter_read(counter);
+        n = 1;
+        if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
+                values[n++] = counter->total_time_enabled +
+                        atomic64_read(&counter->child_total_time_enabled);
+        if (counter->attr.read_format & PERF_FORMAT_TOTAL_TIME_RUNNING)
+                values[n++] = counter->total_time_running +
+                        atomic64_read(&counter->child_total_time_running);
+        if (counter->attr.read_format & PERF_FORMAT_ID)
+                values[n++] = counter->id;
+        mutex_unlock(&counter->child_mutex);
+
+        if (count < n * sizeof(u64))
+                return -EINVAL;
+        count = n * sizeof(u64);
+
+        if (copy_to_user(buf, values, count))
+                return -EFAULT;
+
+        return count;
+}
+
+static ssize_t
+perf_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
+{
+        struct perf_counter *counter = file->private_data;
+
+        return perf_read_hw(counter, buf, count);
+}
+
+static unsigned int perf_poll(struct file *file, poll_table *wait)
+{
+        struct perf_counter *counter = file->private_data;
+        struct perf_mmap_data *data;
+        unsigned int events = POLL_HUP;
+
+        rcu_read_lock();
+        data = rcu_dereference(counter->data);
+        if (data)
+                events = atomic_xchg(&data->poll, 0);
+        rcu_read_unlock();
+
+        poll_wait(file, &counter->waitq, wait);
+
+        return events;
+}
+
+static void perf_counter_reset(struct perf_counter *counter)
+{
+        (void)perf_counter_read(counter);
+        atomic64_set(&counter->count, 0);
+        perf_counter_update_userpage(counter);
+}
+
+static void perf_counter_for_each_sibling(struct perf_counter *counter,
+                                          void (*func)(struct perf_counter *))
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        struct perf_counter *sibling;
+
+        WARN_ON_ONCE(ctx->parent_ctx);
+        mutex_lock(&ctx->mutex);
+        counter = counter->group_leader;
+
+        func(counter);
+        list_for_each_entry(sibling, &counter->sibling_list, list_entry)
+                func(sibling);
+        mutex_unlock(&ctx->mutex);
+}
+
+/*
+ * Holding the top-level counter's child_mutex means that any
+ * descendant process that has inherited this counter will block
+ * in sync_child_counter if it goes to exit, thus satisfying the
+ * task existence requirements of perf_counter_enable/disable.
+ */
+static void perf_counter_for_each_child(struct perf_counter *counter,
+                                        void (*func)(struct perf_counter *))
+{
+        struct perf_counter *child;
+
+        WARN_ON_ONCE(counter->ctx->parent_ctx);
+        mutex_lock(&counter->child_mutex);
+        func(counter);
+        list_for_each_entry(child, &counter->child_list, child_list)
+                func(child);
+        mutex_unlock(&counter->child_mutex);
+}
+
+static void perf_counter_for_each(struct perf_counter *counter,
+                                  void (*func)(struct perf_counter *))
+{
+        struct perf_counter *child;
+
+        WARN_ON_ONCE(counter->ctx->parent_ctx);
+        mutex_lock(&counter->child_mutex);
+        perf_counter_for_each_sibling(counter, func);
+        list_for_each_entry(child, &counter->child_list, child_list)
+                perf_counter_for_each_sibling(child, func);
+        mutex_unlock(&counter->child_mutex);
+}
+
+static int perf_counter_period(struct perf_counter *counter, u64 __user *arg)
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        unsigned long size;
+        int ret = 0;
+        u64 value;
+
+        if (!counter->attr.sample_period)
+                return -EINVAL;
+
+        size = copy_from_user(&value, arg, sizeof(value));
+        if (size != sizeof(value))
+                return -EFAULT;
+
+        if (!value)
+                return -EINVAL;
+
+        spin_lock_irq(&ctx->lock);
+        if (counter->attr.freq) {
+                if (value > sysctl_perf_counter_sample_rate) {
+                        ret = -EINVAL;
+                        goto unlock;
+                }
+
+                counter->attr.sample_freq = value;
+        } else {
+                perf_log_period(counter, value);
+
+                counter->attr.sample_period = value;
+                counter->hw.sample_period = value;
+        }
+unlock:
+        spin_unlock_irq(&ctx->lock);
+
+        return ret;
+}
+
+static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+        struct perf_counter *counter = file->private_data;
+        void (*func)(struct perf_counter *);
+        u32 flags = arg;
+
+        switch (cmd) {
+        case PERF_COUNTER_IOC_ENABLE:
+                func = perf_counter_enable;
+                break;
+        case PERF_COUNTER_IOC_DISABLE:
+                func = perf_counter_disable;
+                break;
+        case PERF_COUNTER_IOC_RESET:
+                func = perf_counter_reset;
+                break;
+
+        case PERF_COUNTER_IOC_REFRESH:
+                return perf_counter_refresh(counter, arg);
+
+        case PERF_COUNTER_IOC_PERIOD:
+                return perf_counter_period(counter, (u64 __user *)arg);
+
+        default:
+                return -ENOTTY;
+        }
+
+        if (flags & PERF_IOC_FLAG_GROUP)
+                perf_counter_for_each(counter, func);
+        else
+                perf_counter_for_each_child(counter, func);
+
+        return 0;
+}
+
+int perf_counter_task_enable(void)
+{
+        struct perf_counter *counter;
+
+        mutex_lock(&current->perf_counter_mutex);
+        list_for_each_entry(counter, &current->perf_counter_list, owner_entry)
+                perf_counter_for_each_child(counter, perf_counter_enable);
+        mutex_unlock(&current->perf_counter_mutex);
+
+        return 0;
+}
+
+int perf_counter_task_disable(void)
+{
+        struct perf_counter *counter;
+
+        mutex_lock(&current->perf_counter_mutex);
+        list_for_each_entry(counter, &current->perf_counter_list, owner_entry)
+                perf_counter_for_each_child(counter, perf_counter_disable);
+        mutex_unlock(&current->perf_counter_mutex);
+
+        return 0;
+}
+
+/*
+ * Callers need to ensure there can be no nesting of this function, otherwise
+ * the seqlock logic goes bad. We can not serialize this because the arch
+ * code calls this from NMI context.
+ */
+void perf_counter_update_userpage(struct perf_counter *counter)
+{
+        struct perf_counter_mmap_page *userpg;
+        struct perf_mmap_data *data;
+
+        rcu_read_lock();
+        data = rcu_dereference(counter->data);
+        if (!data)
+                goto unlock;
+
+        userpg = data->user_page;
+
+        /*
+         * Disable preemption so as to not let the corresponding user-space
+         * spin too long if we get preempted.
+         */
+        preempt_disable();
+        ++userpg->lock;
+        barrier();
+        userpg->index = counter->hw.idx;
+        userpg->offset = atomic64_read(&counter->count);
+        if (counter->state == PERF_COUNTER_STATE_ACTIVE)
+                userpg->offset -= atomic64_read(&counter->hw.prev_count);
+
+        barrier();
+        ++userpg->lock;
+        preempt_enable();
+unlock:
+        rcu_read_unlock();
+}
+
+static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+        struct perf_counter *counter = vma->vm_file->private_data;
+        struct perf_mmap_data *data;
+        int ret = VM_FAULT_SIGBUS;
+
+        rcu_read_lock();
+        data = rcu_dereference(counter->data);
+        if (!data)
+                goto unlock;
+
+        if (vmf->pgoff == 0) {
+                vmf->page = virt_to_page(data->user_page);
+        } else {
+                int nr = vmf->pgoff - 1;
+
+                if ((unsigned)nr > data->nr_pages)
+                        goto unlock;
+
+                vmf->page = virt_to_page(data->data_pages[nr]);
+        }
+        get_page(vmf->page);
+        ret = 0;
+unlock:
+        rcu_read_unlock();
+
+        return ret;
+}
+
+static int perf_mmap_data_alloc(struct perf_counter *counter, int nr_pages)
+{
+        struct perf_mmap_data *data;
+        unsigned long size;
+        int i;
+
+        WARN_ON(atomic_read(&counter->mmap_count));
+
+        size = sizeof(struct perf_mmap_data);
+        size += nr_pages * sizeof(void *);
+
+        data = kzalloc(size, GFP_KERNEL);
+        if (!data)
+                goto fail;
+
+        data->user_page = (void *)get_zeroed_page(GFP_KERNEL);
+        if (!data->user_page)
+                goto fail_user_page;
+
+        for (i = 0; i < nr_pages; i++) {
+                data->data_pages[i] = (void *)get_zeroed_page(GFP_KERNEL);
+                if (!data->data_pages[i])
+                        goto fail_data_pages;
+        }
+
+        data->nr_pages = nr_pages;
+        atomic_set(&data->lock, -1);
+
+        rcu_assign_pointer(counter->data, data);
+
+        return 0;
+
+fail_data_pages:
+        for (i--; i >= 0; i--)
+                free_page((unsigned long)data->data_pages[i]);
+
+        free_page((unsigned long)data->user_page);
+
+fail_user_page:
+        kfree(data);
+
+fail:
+        return -ENOMEM;
+}
+
+static void __perf_mmap_data_free(struct rcu_head *rcu_head)
+{
+        struct perf_mmap_data *data;
+        int i;
+
+        data = container_of(rcu_head, struct perf_mmap_data, rcu_head);
+
+        free_page((unsigned long)data->user_page);
+        for (i = 0; i < data->nr_pages; i++)
+                free_page((unsigned long)data->data_pages[i]);
+        kfree(data);
+}
+
+static void perf_mmap_data_free(struct perf_counter *counter)
+{
+        struct perf_mmap_data *data = counter->data;
+
+        WARN_ON(atomic_read(&counter->mmap_count));
+
+        rcu_assign_pointer(counter->data, NULL);
+        call_rcu(&data->rcu_head, __perf_mmap_data_free);
+}
+
+static void perf_mmap_open(struct vm_area_struct *vma)
+{
+        struct perf_counter *counter = vma->vm_file->private_data;
+
+        atomic_inc(&counter->mmap_count);
+}
+
+static void perf_mmap_close(struct vm_area_struct *vma)
+{
+        struct perf_counter *counter = vma->vm_file->private_data;
+
+        WARN_ON_ONCE(counter->ctx->parent_ctx);
+        if (atomic_dec_and_mutex_lock(&counter->mmap_count, &counter->mmap_mutex)) {
+                struct user_struct *user = current_user();
+
+                atomic_long_sub(counter->data->nr_pages + 1, &user->locked_vm);
+                vma->vm_mm->locked_vm -= counter->data->nr_locked;
+                perf_mmap_data_free(counter);
+                mutex_unlock(&counter->mmap_mutex);
+        }
+}
+
+static struct vm_operations_struct perf_mmap_vmops = {
+        .open  = perf_mmap_open,
+        .close = perf_mmap_close,
+        .fault = perf_mmap_fault,
+};
+
+static int perf_mmap(struct file *file, struct vm_area_struct *vma)
+{
+        struct perf_counter *counter = file->private_data;
+        unsigned long user_locked, user_lock_limit;
+        struct user_struct *user = current_user();
+        unsigned long locked, lock_limit;
+        unsigned long vma_size;
+        unsigned long nr_pages;
+        long user_extra, extra;
+        int ret = 0;
+
+        if (!(vma->vm_flags & VM_SHARED) || (vma->vm_flags & VM_WRITE))
+                return -EINVAL;
+
+        vma_size = vma->vm_end - vma->vm_start;
+        nr_pages = (vma_size / PAGE_SIZE) - 1;
+
+        /*
+         * If we have data pages ensure they're a power-of-two number, so we
+         * can do bitmasks instead of modulo.
+         */
+        if (nr_pages != 0 && !is_power_of_2(nr_pages))
+                return -EINVAL;
+
+        if (vma_size != PAGE_SIZE * (1 + nr_pages))
+                return -EINVAL;
+
+        if (vma->vm_pgoff != 0)
+                return -EINVAL;
+
+        WARN_ON_ONCE(counter->ctx->parent_ctx);
+        mutex_lock(&counter->mmap_mutex);
+        if (atomic_inc_not_zero(&counter->mmap_count)) {
+                if (nr_pages != counter->data->nr_pages)
+                        ret = -EINVAL;
+                goto unlock;
+        }
+
+        user_extra = nr_pages + 1;
+        user_lock_limit = sysctl_perf_counter_mlock >> (PAGE_SHIFT - 10);
+
+        /*
+         * Increase the limit linearly with more CPUs:
+         */
+        user_lock_limit *= num_online_cpus();
+
+        user_locked = atomic_long_read(&user->locked_vm) + user_extra;
+
+        extra = 0;
+        if (user_locked > user_lock_limit)
+                extra = user_locked - user_lock_limit;
+
+        lock_limit = current->signal->rlim[RLIMIT_MEMLOCK].rlim_cur;
+        lock_limit >>= PAGE_SHIFT;
+        locked = vma->vm_mm->locked_vm + extra;
+
+        if ((locked > lock_limit) && !capable(CAP_IPC_LOCK)) {
+                ret = -EPERM;
+                goto unlock;
+        }
+
+        WARN_ON(counter->data);
+        ret = perf_mmap_data_alloc(counter, nr_pages);
+        if (ret)
+                goto unlock;
+
+        atomic_set(&counter->mmap_count, 1);
+        atomic_long_add(user_extra, &user->locked_vm);
+        vma->vm_mm->locked_vm += extra;
+        counter->data->nr_locked = extra;
+unlock:
+        mutex_unlock(&counter->mmap_mutex);
+
+        vma->vm_flags &= ~VM_MAYWRITE;
+        vma->vm_flags |= VM_RESERVED;
+        vma->vm_ops = &perf_mmap_vmops;
+
+        return ret;
+}
+
+static int perf_fasync(int fd, struct file *filp, int on)
+{
+        struct inode *inode = filp->f_path.dentry->d_inode;
+        struct perf_counter *counter = filp->private_data;
+        int retval;
+
+        mutex_lock(&inode->i_mutex);
+        retval = fasync_helper(fd, filp, on, &counter->fasync);
+        mutex_unlock(&inode->i_mutex);
+
+        if (retval < 0)
+                return retval;
+
+        return 0;
+}
+
+static const struct file_operations perf_fops = {
+        .release                = perf_release,
+        .read                   = perf_read,
+        .poll                   = perf_poll,
+        .unlocked_ioctl         = perf_ioctl,
+        .compat_ioctl           = perf_ioctl,
+        .mmap                   = perf_mmap,
+        .fasync                 = perf_fasync,
+};
+
+/*
+ * Perf counter wakeup
+ *
+ * If there's data, ensure we set the poll() state and publish everything
+ * to user-space before waking everybody up.
+ */
+
+void perf_counter_wakeup(struct perf_counter *counter)
+{
+        wake_up_all(&counter->waitq);
+
+        if (counter->pending_kill) {
+                kill_fasync(&counter->fasync, SIGIO, counter->pending_kill);
+                counter->pending_kill = 0;
+        }
+}
+
+/*
+ * Pending wakeups
+ *
+ * Handle the case where we need to wakeup up from NMI (or rq->lock) context.
+ *
+ * The NMI bit means we cannot possibly take locks. Therefore, maintain a
+ * single linked list and use cmpxchg() to add entries lockless.
+ */
+
+static void perf_pending_counter(struct perf_pending_entry *entry)
+{
+        struct perf_counter *counter = container_of(entry,
+                        struct perf_counter, pending);
+
+        if (counter->pending_disable) {
+                counter->pending_disable = 0;
+                perf_counter_disable(counter);
+        }
+
+        if (counter->pending_wakeup) {
+                counter->pending_wakeup = 0;
+                perf_counter_wakeup(counter);
+        }
+}
+
+#define PENDING_TAIL ((struct perf_pending_entry *)-1UL)
+
+static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
+        PENDING_TAIL,
+};
+
+static void perf_pending_queue(struct perf_pending_entry *entry,
+                               void (*func)(struct perf_pending_entry *))
+{
+        struct perf_pending_entry **head;
+
+        if (cmpxchg(&entry->next, NULL, PENDING_TAIL) != NULL)
+                return;
+
+        entry->func = func;
+
+        head = &get_cpu_var(perf_pending_head);
+
+        do {
+                entry->next = *head;
+        } while (cmpxchg(head, entry->next, entry) != entry->next);
+
+        set_perf_counter_pending();
+
+        put_cpu_var(perf_pending_head);
+}
+
+static int __perf_pending_run(void)
+{
+        struct perf_pending_entry *list;
+        int nr = 0;
+
+        list = xchg(&__get_cpu_var(perf_pending_head), PENDING_TAIL);
+        while (list != PENDING_TAIL) {
+                void (*func)(struct perf_pending_entry *);
+                struct perf_pending_entry *entry = list;
+
+                list = list->next;
+
+                func = entry->func;
+                entry->next = NULL;
+                /*
+                 * Ensure we observe the unqueue before we issue the wakeup,
+                 * so that we won't be waiting forever.
+                 * -- see perf_not_pending().
+                 */
+                smp_wmb();
+
+                func(entry);
+                nr++;
+        }
+
+        return nr;
+}
+
+static inline int perf_not_pending(struct perf_counter *counter)
+{
+        /*
+         * If we flush on whatever cpu we run, there is a chance we don't
+         * need to wait.
+         */
+        get_cpu();
+        __perf_pending_run();
+        put_cpu();
+
+        /*
+         * Ensure we see the proper queue state before going to sleep
+         * so that we do not miss the wakeup. -- see perf_pending_handle()
+         */
+        smp_rmb();
+        return counter->pending.next == NULL;
+}
+
+static void perf_pending_sync(struct perf_counter *counter)
+{
+        wait_event(counter->waitq, perf_not_pending(counter));
+}
+
+void perf_counter_do_pending(void)
+{
+        __perf_pending_run();
+}
+
+/*
+ * Callchain support -- arch specific
+ */
+
+__weak struct perf_callchain_entry *perf_callchain(struct pt_regs *regs)
+{
+        return NULL;
+}
+
+/*
+ * Output
+ */
+
+struct perf_output_handle {
+        struct perf_counter     *counter;
+        struct perf_mmap_data   *data;
+        unsigned long           head;
+        unsigned long           offset;
+        int                     nmi;
+        int                     overflow;
+        int                     locked;
+        unsigned long           flags;
+};
+
+static void perf_output_wakeup(struct perf_output_handle *handle)
+{
+        atomic_set(&handle->data->poll, POLL_IN);
+
+        if (handle->nmi) {
+                handle->counter->pending_wakeup = 1;
+                perf_pending_queue(&handle->counter->pending,
+                                   perf_pending_counter);
+        } else
+                perf_counter_wakeup(handle->counter);
+}
+
+/*
+ * Curious locking construct.
+ *
+ * We need to ensure a later event doesn't publish a head when a former
+ * event isn't done writing. However since we need to deal with NMIs we
+ * cannot fully serialize things.
+ *
+ * What we do is serialize between CPUs so we only have to deal with NMI
+ * nesting on a single CPU.
+ *
+ * We only publish the head (and generate a wakeup) when the outer-most
+ * event completes.
+ */
+static void perf_output_lock(struct perf_output_handle *handle)
+{
+        struct perf_mmap_data *data = handle->data;
+        int cpu;
+
+        handle->locked = 0;
+
+        local_irq_save(handle->flags);
+        cpu = smp_processor_id();
+
+        if (in_nmi() && atomic_read(&data->lock) == cpu)
+                return;
+
+        while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
+                cpu_relax();
+
+        handle->locked = 1;
+}
+
+static void perf_output_unlock(struct perf_output_handle *handle)
+{
+        struct perf_mmap_data *data = handle->data;
+        unsigned long head;
+        int cpu;
+
+        data->done_head = data->head;
+
+        if (!handle->locked)
+                goto out;
+
+again:
+        /*
+         * The xchg implies a full barrier that ensures all writes are done
+         * before we publish the new head, matched by a rmb() in userspace when
+         * reading this position.
+         */
+        while ((head = atomic_long_xchg(&data->done_head, 0)))
+                data->user_page->data_head = head;
+
+        /*
+         * NMI can happen here, which means we can miss a done_head update.
+         */
+
+        cpu = atomic_xchg(&data->lock, -1);
+        WARN_ON_ONCE(cpu != smp_processor_id());
+
+        /*
+         * Therefore we have to validate we did not indeed do so.
+         */
+        if (unlikely(atomic_long_read(&data->done_head))) {
+                /*
+                 * Since we had it locked, we can lock it again.
+                 */
+                while (atomic_cmpxchg(&data->lock, -1, cpu) != -1)
+                        cpu_relax();
+
+                goto again;
+        }
+
+        if (atomic_xchg(&data->wakeup, 0))
+                perf_output_wakeup(handle);
+out:
+        local_irq_restore(handle->flags);
+}
+
+static int perf_output_begin(struct perf_output_handle *handle,
+                             struct perf_counter *counter, unsigned int size,
+                             int nmi, int overflow)
+{
+        struct perf_mmap_data *data;
+        unsigned int offset, head;
+
+        /*
+         * For inherited counters we send all the output towards the parent.
+         */
+        if (counter->parent)
+                counter = counter->parent;
+
+        rcu_read_lock();
+        data = rcu_dereference(counter->data);
+        if (!data)
+                goto out;
+
+        handle->data     = data;
+        handle->counter  = counter;
+        handle->nmi      = nmi;
+        handle->overflow = overflow;
+
+        if (!data->nr_pages)
+                goto fail;
+
+        perf_output_lock(handle);
+
+        do {
+                offset = head = atomic_long_read(&data->head);
+                head += size;
+        } while (atomic_long_cmpxchg(&data->head, offset, head) != offset);
+
+        handle->offset  = offset;
+        handle->head    = head;
+
+        if ((offset >> PAGE_SHIFT) != (head >> PAGE_SHIFT))
+                atomic_set(&data->wakeup, 1);
+
+        return 0;
+
+fail:
+        perf_output_wakeup(handle);
+out:
+        rcu_read_unlock();
+
+        return -ENOSPC;
+}
+
+static void perf_output_copy(struct perf_output_handle *handle,
+                             const void *buf, unsigned int len)
+{
+        unsigned int pages_mask;
+        unsigned int offset;
+        unsigned int size;
+        void **pages;
+
+        offset          = handle->offset;
+        pages_mask      = handle->data->nr_pages - 1;
+        pages           = handle->data->data_pages;
+
+        do {
+                unsigned int page_offset;
+                int nr;
+
+                nr          = (offset >> PAGE_SHIFT) & pages_mask;
+                page_offset = offset & (PAGE_SIZE - 1);
+                size        = min_t(unsigned int, PAGE_SIZE - page_offset, len);
+
+                memcpy(pages[nr] + page_offset, buf, size);
+
+                len         -= size;
+                buf         += size;
+                offset      += size;
+        } while (len);
+
+        handle->offset = offset;
+
+        /*
+         * Check we didn't copy past our reservation window, taking the
+         * possible unsigned int wrap into account.
+         */
+        WARN_ON_ONCE(((long)(handle->head - handle->offset)) < 0);
+}
+
+#define perf_output_put(handle, x) \
+        perf_output_copy((handle), &(x), sizeof(x))
+
+static void perf_output_end(struct perf_output_handle *handle)
+{
+        struct perf_counter *counter = handle->counter;
+        struct perf_mmap_data *data = handle->data;
+
+        int wakeup_events = counter->attr.wakeup_events;
+
+        if (handle->overflow && wakeup_events) {
+                int events = atomic_inc_return(&data->events);
+                if (events >= wakeup_events) {
+                        atomic_sub(wakeup_events, &data->events);
+                        atomic_set(&data->wakeup, 1);
+                }
+        }
+
+        perf_output_unlock(handle);
+        rcu_read_unlock();
+}
+
+static u32 perf_counter_pid(struct perf_counter *counter, struct task_struct *p)
+{
+        /*
+         * only top level counters have the pid namespace they were created in
+         */
+        if (counter->parent)
+                counter = counter->parent;
+
+        return task_tgid_nr_ns(p, counter->ns);
+}
+
+static u32 perf_counter_tid(struct perf_counter *counter, struct task_struct *p)
+{
+        /*
+         * only top level counters have the pid namespace they were created in
+         */
+        if (counter->parent)
+                counter = counter->parent;
+
+        return task_pid_nr_ns(p, counter->ns);
+}
+
+static void perf_counter_output(struct perf_counter *counter, int nmi,
+                                struct perf_sample_data *data)
+{
+        int ret;
+        u64 sample_type = counter->attr.sample_type;
+        struct perf_output_handle handle;
+        struct perf_event_header header;
+        u64 ip;
+        struct {
+                u32 pid, tid;
+        } tid_entry;
+        struct {
+                u64 id;
+                u64 counter;
+        } group_entry;
+        struct perf_callchain_entry *callchain = NULL;
+        int callchain_size = 0;
+        u64 time;
+        struct {
+                u32 cpu, reserved;
+        } cpu_entry;
+
+        header.type = 0;
+        header.size = sizeof(header);
+
+        header.misc = PERF_EVENT_MISC_OVERFLOW;
+        header.misc |= perf_misc_flags(data->regs);
+
+        if (sample_type & PERF_SAMPLE_IP) {
+                ip = perf_instruction_pointer(data->regs);
+                header.type |= PERF_SAMPLE_IP;
+                header.size += sizeof(ip);
+        }
+
+        if (sample_type & PERF_SAMPLE_TID) {
+                /* namespace issues */
+                tid_entry.pid = perf_counter_pid(counter, current);
+                tid_entry.tid = perf_counter_tid(counter, current);
+
+                header.type |= PERF_SAMPLE_TID;
+                header.size += sizeof(tid_entry);
+        }
+
+        if (sample_type & PERF_SAMPLE_TIME) {
+                /*
+                 * Maybe do better on x86 and provide cpu_clock_nmi()
+                 */
+                time = sched_clock();
+
+                header.type |= PERF_SAMPLE_TIME;
+                header.size += sizeof(u64);
+        }
+
+        if (sample_type & PERF_SAMPLE_ADDR) {
+                header.type |= PERF_SAMPLE_ADDR;
+                header.size += sizeof(u64);
+        }
+
+        if (sample_type & PERF_SAMPLE_ID) {
+                header.type |= PERF_SAMPLE_ID;
+                header.size += sizeof(u64);
+        }
+
+        if (sample_type & PERF_SAMPLE_CPU) {
+                header.type |= PERF_SAMPLE_CPU;
+                header.size += sizeof(cpu_entry);
+
+                cpu_entry.cpu = raw_smp_processor_id();
+        }
+
+        if (sample_type & PERF_SAMPLE_PERIOD) {
+                header.type |= PERF_SAMPLE_PERIOD;
+                header.size += sizeof(u64);
+        }
+
+        if (sample_type & PERF_SAMPLE_GROUP) {
+                header.type |= PERF_SAMPLE_GROUP;
+                header.size += sizeof(u64) +
+                        counter->nr_siblings * sizeof(group_entry);
+        }
+
+        if (sample_type & PERF_SAMPLE_CALLCHAIN) {
+                callchain = perf_callchain(data->regs);
+
+                if (callchain) {
+                        callchain_size = (1 + callchain->nr) * sizeof(u64);
+
+                        header.type |= PERF_SAMPLE_CALLCHAIN;
+                        header.size += callchain_size;
+                }
+        }
+
+        ret = perf_output_begin(&handle, counter, header.size, nmi, 1);
+        if (ret)
+                return;
+
+        perf_output_put(&handle, header);
+
+        if (sample_type & PERF_SAMPLE_IP)
+                perf_output_put(&handle, ip);
+
+        if (sample_type & PERF_SAMPLE_TID)
+                perf_output_put(&handle, tid_entry);
+
+        if (sample_type & PERF_SAMPLE_TIME)
+                perf_output_put(&handle, time);
+
+        if (sample_type & PERF_SAMPLE_ADDR)
+                perf_output_put(&handle, data->addr);
+
+        if (sample_type & PERF_SAMPLE_ID)
+                perf_output_put(&handle, counter->id);
+
+        if (sample_type & PERF_SAMPLE_CPU)
+                perf_output_put(&handle, cpu_entry);
+
+        if (sample_type & PERF_SAMPLE_PERIOD)
+                perf_output_put(&handle, data->period);
+
+        /*
+         * XXX PERF_SAMPLE_GROUP vs inherited counters seems difficult.
+         */
+        if (sample_type & PERF_SAMPLE_GROUP) {
+                struct perf_counter *leader, *sub;
+                u64 nr = counter->nr_siblings;
+
+                perf_output_put(&handle, nr);
+
+                leader = counter->group_leader;
+                list_for_each_entry(sub, &leader->sibling_list, list_entry) {
+                        if (sub != counter)
+                                sub->pmu->read(sub);
+
+                        group_entry.id = sub->id;
+                        group_entry.counter = atomic64_read(&sub->count);
+
+                        perf_output_put(&handle, group_entry);
+                }
+        }
+
+        if (callchain)
+                perf_output_copy(&handle, callchain, callchain_size);
+
+        perf_output_end(&handle);
+}
+
+/*
+ * fork tracking
+ */
+
+struct perf_fork_event {
+        struct task_struct      *task;
+
+        struct {
+                struct perf_event_header        header;
+
+                u32                             pid;
+                u32                             ppid;
+        } event;
+};
+
+static void perf_counter_fork_output(struct perf_counter *counter,
+                                     struct perf_fork_event *fork_event)
+{
+        struct perf_output_handle handle;
+        int size = fork_event->event.header.size;
+        struct task_struct *task = fork_event->task;
+        int ret = perf_output_begin(&handle, counter, size, 0, 0);
+
+        if (ret)
+                return;
+
+        fork_event->event.pid = perf_counter_pid(counter, task);
+        fork_event->event.ppid = perf_counter_pid(counter, task->real_parent);
+
+        perf_output_put(&handle, fork_event->event);
+        perf_output_end(&handle);
+}
+
+static int perf_counter_fork_match(struct perf_counter *counter)
+{
+        if (counter->attr.comm || counter->attr.mmap)
+                return 1;
+
+        return 0;
+}
+
+static void perf_counter_fork_ctx(struct perf_counter_context *ctx,
+                                  struct perf_fork_event *fork_event)
+{
+        struct perf_counter *counter;
+
+        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
+                return;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
+                if (perf_counter_fork_match(counter))
+                        perf_counter_fork_output(counter, fork_event);
+        }
+        rcu_read_unlock();
+}
+
+static void perf_counter_fork_event(struct perf_fork_event *fork_event)
+{
+        struct perf_cpu_context *cpuctx;
+        struct perf_counter_context *ctx;
+
+        cpuctx = &get_cpu_var(perf_cpu_context);
+        perf_counter_fork_ctx(&cpuctx->ctx, fork_event);
+        put_cpu_var(perf_cpu_context);
+
+        rcu_read_lock();
+        /*
+         * doesn't really matter which of the child contexts the
+         * events ends up in.
+         */
+        ctx = rcu_dereference(current->perf_counter_ctxp);
+        if (ctx)
+                perf_counter_fork_ctx(ctx, fork_event);
+        rcu_read_unlock();
+}
+
+void perf_counter_fork(struct task_struct *task)
+{
+        struct perf_fork_event fork_event;
+
+        if (!atomic_read(&nr_comm_counters) &&
+            !atomic_read(&nr_mmap_counters))
+                return;
+
+        fork_event = (struct perf_fork_event){
+                .task   = task,
+                .event  = {
+                        .header = {
+                                .type = PERF_EVENT_FORK,
+                                .size = sizeof(fork_event.event),
+                        },
+                },
+        };
+
+        perf_counter_fork_event(&fork_event);
+}
+
+/*
+ * comm tracking
+ */
+
+struct perf_comm_event {
+        struct task_struct      *task;
+        char                    *comm;
+        int                     comm_size;
+
+        struct {
+                struct perf_event_header        header;
+
+                u32                             pid;
+                u32                             tid;
+        } event;
+};
+
+static void perf_counter_comm_output(struct perf_counter *counter,
+                                     struct perf_comm_event *comm_event)
+{
+        struct perf_output_handle handle;
+        int size = comm_event->event.header.size;
+        int ret = perf_output_begin(&handle, counter, size, 0, 0);
+
+        if (ret)
+                return;
+
+        comm_event->event.pid = perf_counter_pid(counter, comm_event->task);
+        comm_event->event.tid = perf_counter_tid(counter, comm_event->task);
+
+        perf_output_put(&handle, comm_event->event);
+        perf_output_copy(&handle, comm_event->comm,
+                                   comm_event->comm_size);
+        perf_output_end(&handle);
+}
+
+static int perf_counter_comm_match(struct perf_counter *counter)
+{
+        if (counter->attr.comm)
+                return 1;
+
+        return 0;
+}
+
+static void perf_counter_comm_ctx(struct perf_counter_context *ctx,
+                                  struct perf_comm_event *comm_event)
+{
+        struct perf_counter *counter;
+
+        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
+                return;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
+                if (perf_counter_comm_match(counter))
+                        perf_counter_comm_output(counter, comm_event);
+        }
+        rcu_read_unlock();
+}
+
+static void perf_counter_comm_event(struct perf_comm_event *comm_event)
+{
+        struct perf_cpu_context *cpuctx;
+        struct perf_counter_context *ctx;
+        unsigned int size;
+        char *comm = comm_event->task->comm;
+
+        size = ALIGN(strlen(comm)+1, sizeof(u64));
+
+        comm_event->comm = comm;
+        comm_event->comm_size = size;
+
+        comm_event->event.header.size = sizeof(comm_event->event) + size;
+
+        cpuctx = &get_cpu_var(perf_cpu_context);
+        perf_counter_comm_ctx(&cpuctx->ctx, comm_event);
+        put_cpu_var(perf_cpu_context);
+
+        rcu_read_lock();
+        /*
+         * doesn't really matter which of the child contexts the
+         * events ends up in.
+         */
+        ctx = rcu_dereference(current->perf_counter_ctxp);
+        if (ctx)
+                perf_counter_comm_ctx(ctx, comm_event);
+        rcu_read_unlock();
+}
+
+void perf_counter_comm(struct task_struct *task)
+{
+        struct perf_comm_event comm_event;
+
+        if (!atomic_read(&nr_comm_counters))
+                return;
+
+        comm_event = (struct perf_comm_event){
+                .task   = task,
+                .event  = {
+                        .header = { .type = PERF_EVENT_COMM, },
+                },
+        };
+
+        perf_counter_comm_event(&comm_event);
+}
+
+/*
+ * mmap tracking
+ */
+
+struct perf_mmap_event {
+        struct vm_area_struct   *vma;
+
+        const char              *file_name;
+        int                     file_size;
+
+        struct {
+                struct perf_event_header        header;
+
+                u32                             pid;
+                u32                             tid;
+                u64                             start;
+                u64                             len;
+                u64                             pgoff;
+        } event;
+};
+
+static void perf_counter_mmap_output(struct perf_counter *counter,
+                                     struct perf_mmap_event *mmap_event)
+{
+        struct perf_output_handle handle;
+        int size = mmap_event->event.header.size;
+        int ret = perf_output_begin(&handle, counter, size, 0, 0);
+
+        if (ret)
+                return;
+
+        mmap_event->event.pid = perf_counter_pid(counter, current);
+        mmap_event->event.tid = perf_counter_tid(counter, current);
+
+        perf_output_put(&handle, mmap_event->event);
+        perf_output_copy(&handle, mmap_event->file_name,
+                                   mmap_event->file_size);
+        perf_output_end(&handle);
+}
+
+static int perf_counter_mmap_match(struct perf_counter *counter,
+                                   struct perf_mmap_event *mmap_event)
+{
+        if (counter->attr.mmap)
+                return 1;
+
+        return 0;
+}
+
+static void perf_counter_mmap_ctx(struct perf_counter_context *ctx,
+                                  struct perf_mmap_event *mmap_event)
+{
+        struct perf_counter *counter;
+
+        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
+                return;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
+                if (perf_counter_mmap_match(counter, mmap_event))
+                        perf_counter_mmap_output(counter, mmap_event);
+        }
+        rcu_read_unlock();
+}
+
+static void perf_counter_mmap_event(struct perf_mmap_event *mmap_event)
+{
+        struct perf_cpu_context *cpuctx;
+        struct perf_counter_context *ctx;
+        struct vm_area_struct *vma = mmap_event->vma;
+        struct file *file = vma->vm_file;
+        unsigned int size;
+        char tmp[16];
+        char *buf = NULL;
+        const char *name;
+
+        if (file) {
+                buf = kzalloc(PATH_MAX, GFP_KERNEL);
+                if (!buf) {
+                        name = strncpy(tmp, "//enomem", sizeof(tmp));
+                        goto got_name;
+                }
+                name = d_path(&file->f_path, buf, PATH_MAX);
+                if (IS_ERR(name)) {
+                        name = strncpy(tmp, "//toolong", sizeof(tmp));
+                        goto got_name;
+                }
+        } else {
+                name = arch_vma_name(mmap_event->vma);
+                if (name)
+                        goto got_name;
+
+                if (!vma->vm_mm) {
+                        name = strncpy(tmp, "[vdso]", sizeof(tmp));
+                        goto got_name;
+                }
+
+                name = strncpy(tmp, "//anon", sizeof(tmp));
+                goto got_name;
+        }
+
+got_name:
+        size = ALIGN(strlen(name)+1, sizeof(u64));
+
+        mmap_event->file_name = name;
+        mmap_event->file_size = size;
+
+        mmap_event->event.header.size = sizeof(mmap_event->event) + size;
+
+        cpuctx = &get_cpu_var(perf_cpu_context);
+        perf_counter_mmap_ctx(&cpuctx->ctx, mmap_event);
+        put_cpu_var(perf_cpu_context);
+
+        rcu_read_lock();
+        /*
+         * doesn't really matter which of the child contexts the
+         * events ends up in.
+         */
+        ctx = rcu_dereference(current->perf_counter_ctxp);
+        if (ctx)
+                perf_counter_mmap_ctx(ctx, mmap_event);
+        rcu_read_unlock();
+
+        kfree(buf);
+}
+
+void __perf_counter_mmap(struct vm_area_struct *vma)
+{
+        struct perf_mmap_event mmap_event;
+
+        if (!atomic_read(&nr_mmap_counters))
+                return;
+
+        mmap_event = (struct perf_mmap_event){
+                .vma    = vma,
+                .event  = {
+                        .header = { .type = PERF_EVENT_MMAP, },
+                        .start  = vma->vm_start,
+                        .len    = vma->vm_end - vma->vm_start,
+                        .pgoff  = vma->vm_pgoff,
+                },
+        };
+
+        perf_counter_mmap_event(&mmap_event);
+}
+
+/*
+ * Log sample_period changes so that analyzing tools can re-normalize the
+ * event flow.
+ */
+
+struct freq_event {
+        struct perf_event_header        header;
+        u64                             time;
+        u64                             id;
+        u64                             period;
+};
+
+static void perf_log_period(struct perf_counter *counter, u64 period)
+{
+        struct perf_output_handle handle;
+        struct freq_event event;
+        int ret;
+
+        if (counter->hw.sample_period == period)
+                return;
+
+        if (counter->attr.sample_type & PERF_SAMPLE_PERIOD)
+                return;
+
+        event = (struct freq_event) {
+                .header = {
+                        .type = PERF_EVENT_PERIOD,
+                        .misc = 0,
+                        .size = sizeof(event),
+                },
+                .time = sched_clock(),
+                .id = counter->id,
+                .period = period,
+        };
+
+        ret = perf_output_begin(&handle, counter, sizeof(event), 1, 0);
+        if (ret)
+                return;
+
+        perf_output_put(&handle, event);
+        perf_output_end(&handle);
+}
+
+/*
+ * IRQ throttle logging
+ */
+
+static void perf_log_throttle(struct perf_counter *counter, int enable)
+{
+        struct perf_output_handle handle;
+        int ret;
+
+        struct {
+                struct perf_event_header        header;
+                u64                             time;
+                u64                             id;
+        } throttle_event = {
+                .header = {
+                        .type = PERF_EVENT_THROTTLE + 1,
+                        .misc = 0,
+                        .size = sizeof(throttle_event),
+                },
+                .time   = sched_clock(),
+                .id     = counter->id,
+        };
+
+        ret = perf_output_begin(&handle, counter, sizeof(throttle_event), 1, 0);
+        if (ret)
+                return;
+
+        perf_output_put(&handle, throttle_event);
+        perf_output_end(&handle);
+}
+
+/*
+ * Generic counter overflow handling.
+ */
+
+int perf_counter_overflow(struct perf_counter *counter, int nmi,
+                          struct perf_sample_data *data)
+{
+        int events = atomic_read(&counter->event_limit);
+        int throttle = counter->pmu->unthrottle != NULL;
+        struct hw_perf_counter *hwc = &counter->hw;
+        int ret = 0;
+
+        if (!throttle) {
+                hwc->interrupts++;
+        } else {
+                if (hwc->interrupts != MAX_INTERRUPTS) {
+                        hwc->interrupts++;
+                        if (HZ * hwc->interrupts >
+                                        (u64)sysctl_perf_counter_sample_rate) {
+                                hwc->interrupts = MAX_INTERRUPTS;
+                                perf_log_throttle(counter, 0);
+                                ret = 1;
+                        }
+                } else {
+                        /*
+                         * Keep re-disabling counters even though on the previous
+                         * pass we disabled it - just in case we raced with a
+                         * sched-in and the counter got enabled again:
+                         */
+                        ret = 1;
+                }
+        }
+
+        if (counter->attr.freq) {
+                u64 now = sched_clock();
+                s64 delta = now - hwc->freq_stamp;
+
+                hwc->freq_stamp = now;
+
+                if (delta > 0 && delta < TICK_NSEC)
+                        perf_adjust_period(counter, NSEC_PER_SEC / (int)delta);
+        }
+
+        /*
+         * XXX event_limit might not quite work as expected on inherited
+         * counters
+         */
+
+        counter->pending_kill = POLL_IN;
+        if (events && atomic_dec_and_test(&counter->event_limit)) {
+                ret = 1;
+                counter->pending_kill = POLL_HUP;
+                if (nmi) {
+                        counter->pending_disable = 1;
+                        perf_pending_queue(&counter->pending,
+                                           perf_pending_counter);
+                } else
+                        perf_counter_disable(counter);
+        }
+
+        perf_counter_output(counter, nmi, data);
+        return ret;
+}
+
+/*
+ * Generic software counter infrastructure
+ */
+
+static void perf_swcounter_update(struct perf_counter *counter)
+{
+        struct hw_perf_counter *hwc = &counter->hw;
+        u64 prev, now;
+        s64 delta;
+
+again:
+        prev = atomic64_read(&hwc->prev_count);
+        now = atomic64_read(&hwc->count);
+        if (atomic64_cmpxchg(&hwc->prev_count, prev, now) != prev)
+                goto again;
+
+        delta = now - prev;
+
+        atomic64_add(delta, &counter->count);
+        atomic64_sub(delta, &hwc->period_left);
+}
+
+static void perf_swcounter_set_period(struct perf_counter *counter)
+{
+        struct hw_perf_counter *hwc = &counter->hw;
+        s64 left = atomic64_read(&hwc->period_left);
+        s64 period = hwc->sample_period;
+
+        if (unlikely(left <= -period)) {
+                left = period;
+                atomic64_set(&hwc->period_left, left);
+                hwc->last_period = period;
+        }
+
+        if (unlikely(left <= 0)) {
+                left += period;
+                atomic64_add(period, &hwc->period_left);
+                hwc->last_period = period;
+        }
+
+        atomic64_set(&hwc->prev_count, -left);
+        atomic64_set(&hwc->count, -left);
+}
+
+static enum hrtimer_restart perf_swcounter_hrtimer(struct hrtimer *hrtimer)
+{
+        enum hrtimer_restart ret = HRTIMER_RESTART;
+        struct perf_sample_data data;
+        struct perf_counter *counter;
+        u64 period;
+
+        counter = container_of(hrtimer, struct perf_counter, hw.hrtimer);
+        counter->pmu->read(counter);
+
+        data.addr = 0;
+        data.regs = get_irq_regs();
+        /*
+         * In case we exclude kernel IPs or are somehow not in interrupt
+         * context, provide the next best thing, the user IP.
+         */
+        if ((counter->attr.exclude_kernel || !data.regs) &&
+                        !counter->attr.exclude_user)
+                data.regs = task_pt_regs(current);
+
+        if (data.regs) {
+                if (perf_counter_overflow(counter, 0, &data))
+                        ret = HRTIMER_NORESTART;
+        }
+
+        period = max_t(u64, 10000, counter->hw.sample_period);
+        hrtimer_forward_now(hrtimer, ns_to_ktime(period));
+
+        return ret;
+}
+
+static void perf_swcounter_overflow(struct perf_counter *counter,
+                                    int nmi, struct pt_regs *regs, u64 addr)
+{
+        struct perf_sample_data data = {
+                .regs   = regs,
+                .addr   = addr,
+                .period = counter->hw.last_period,
+        };
+
+        perf_swcounter_update(counter);
+        perf_swcounter_set_period(counter);
+        if (perf_counter_overflow(counter, nmi, &data))
+                /* soft-disable the counter */
+                ;
+
+}
+
+static int perf_swcounter_is_counting(struct perf_counter *counter)
+{
+        struct perf_counter_context *ctx;
+        unsigned long flags;
+        int count;
+
+        if (counter->state == PERF_COUNTER_STATE_ACTIVE)
+                return 1;
+
+        if (counter->state != PERF_COUNTER_STATE_INACTIVE)
+                return 0;
+
+        /*
+         * If the counter is inactive, it could be just because
+         * its task is scheduled out, or because it's in a group
+         * which could not go on the PMU.  We want to count in
+         * the first case but not the second.  If the context is
+         * currently active then an inactive software counter must
+         * be the second case.  If it's not currently active then
+         * we need to know whether the counter was active when the
+         * context was last active, which we can determine by
+         * comparing counter->tstamp_stopped with ctx->time.
+         *
+         * We are within an RCU read-side critical section,
+         * which protects the existence of *ctx.
+         */
+        ctx = counter->ctx;
+        spin_lock_irqsave(&ctx->lock, flags);
+        count = 1;
+        /* Re-check state now we have the lock */
+        if (counter->state < PERF_COUNTER_STATE_INACTIVE ||
+            counter->ctx->is_active ||
+            counter->tstamp_stopped < ctx->time)
+                count = 0;
+        spin_unlock_irqrestore(&ctx->lock, flags);
+        return count;
+}
+
+static int perf_swcounter_match(struct perf_counter *counter,
+                                enum perf_type_id type,
+                                u32 event, struct pt_regs *regs)
+{
+        if (!perf_swcounter_is_counting(counter))
+                return 0;
+
+        if (counter->attr.type != type)
+                return 0;
+        if (counter->attr.config != event)
+                return 0;
+
+        if (regs) {
+                if (counter->attr.exclude_user && user_mode(regs))
+                        return 0;
+
+                if (counter->attr.exclude_kernel && !user_mode(regs))
+                        return 0;
+        }
+
+        return 1;
+}
+
+static void perf_swcounter_add(struct perf_counter *counter, u64 nr,
+                               int nmi, struct pt_regs *regs, u64 addr)
+{
+        int neg = atomic64_add_negative(nr, &counter->hw.count);
+
+        if (counter->hw.sample_period && !neg && regs)
+                perf_swcounter_overflow(counter, nmi, regs, addr);
+}
+
+static void perf_swcounter_ctx_event(struct perf_counter_context *ctx,
+                                     enum perf_type_id type, u32 event,
+                                     u64 nr, int nmi, struct pt_regs *regs,
+                                     u64 addr)
+{
+        struct perf_counter *counter;
+
+        if (system_state != SYSTEM_RUNNING || list_empty(&ctx->event_list))
+                return;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(counter, &ctx->event_list, event_entry) {
+                if (perf_swcounter_match(counter, type, event, regs))
+                        perf_swcounter_add(counter, nr, nmi, regs, addr);
+        }
+        rcu_read_unlock();
+}
+
+static int *perf_swcounter_recursion_context(struct perf_cpu_context *cpuctx)
+{
+        if (in_nmi())
+                return &cpuctx->recursion[3];
+
+        if (in_irq())
+                return &cpuctx->recursion[2];
+
+        if (in_softirq())
+                return &cpuctx->recursion[1];
+
+        return &cpuctx->recursion[0];
+}
+
+static void __perf_swcounter_event(enum perf_type_id type, u32 event,
+                                   u64 nr, int nmi, struct pt_regs *regs,
+                                   u64 addr)
+{
+        struct perf_cpu_context *cpuctx = &get_cpu_var(perf_cpu_context);
+        int *recursion = perf_swcounter_recursion_context(cpuctx);
+        struct perf_counter_context *ctx;
+
+        if (*recursion)
+                goto out;
+
+        (*recursion)++;
+        barrier();
+
+        perf_swcounter_ctx_event(&cpuctx->ctx, type, event,
+                                 nr, nmi, regs, addr);
+        rcu_read_lock();
+        /*
+         * doesn't really matter which of the child contexts the
+         * events ends up in.
+         */
+        ctx = rcu_dereference(current->perf_counter_ctxp);
+        if (ctx)
+                perf_swcounter_ctx_event(ctx, type, event, nr, nmi, regs, addr);
+        rcu_read_unlock();
+
+        barrier();
+        (*recursion)--;
+
+out:
+        put_cpu_var(perf_cpu_context);
+}
+
+void
+perf_swcounter_event(u32 event, u64 nr, int nmi, struct pt_regs *regs, u64 addr)
+{
+        __perf_swcounter_event(PERF_TYPE_SOFTWARE, event, nr, nmi, regs, addr);
+}
+
+static void perf_swcounter_read(struct perf_counter *counter)
+{
+        perf_swcounter_update(counter);
+}
+
+static int perf_swcounter_enable(struct perf_counter *counter)
+{
+        perf_swcounter_set_period(counter);
+        return 0;
+}
+
+static void perf_swcounter_disable(struct perf_counter *counter)
+{
+        perf_swcounter_update(counter);
+}
+
+static const struct pmu perf_ops_generic = {
+        .enable         = perf_swcounter_enable,
+        .disable        = perf_swcounter_disable,
+        .read           = perf_swcounter_read,
+};
+
+/*
+ * Software counter: cpu wall time clock
+ */
+
+static void cpu_clock_perf_counter_update(struct perf_counter *counter)
+{
+        int cpu = raw_smp_processor_id();
+        s64 prev;
+        u64 now;
+
+        now = cpu_clock(cpu);
+        prev = atomic64_read(&counter->hw.prev_count);
+        atomic64_set(&counter->hw.prev_count, now);
+        atomic64_add(now - prev, &counter->count);
+}
+
+static int cpu_clock_perf_counter_enable(struct perf_counter *counter)
+{
+        struct hw_perf_counter *hwc = &counter->hw;
+        int cpu = raw_smp_processor_id();
+
+        atomic64_set(&hwc->prev_count, cpu_clock(cpu));
+        hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+        hwc->hrtimer.function = perf_swcounter_hrtimer;
+        if (hwc->sample_period) {
+                u64 period = max_t(u64, 10000, hwc->sample_period);
+                __hrtimer_start_range_ns(&hwc->hrtimer,
+                                ns_to_ktime(period), 0,
+                                HRTIMER_MODE_REL, 0);
+        }
+
+        return 0;
+}
+
+static void cpu_clock_perf_counter_disable(struct perf_counter *counter)
+{
+        if (counter->hw.sample_period)
+                hrtimer_cancel(&counter->hw.hrtimer);
+        cpu_clock_perf_counter_update(counter);
+}
+
+static void cpu_clock_perf_counter_read(struct perf_counter *counter)
+{
+        cpu_clock_perf_counter_update(counter);
+}
+
+static const struct pmu perf_ops_cpu_clock = {
+        .enable         = cpu_clock_perf_counter_enable,
+        .disable        = cpu_clock_perf_counter_disable,
+        .read           = cpu_clock_perf_counter_read,
+};
+
+/*
+ * Software counter: task time clock
+ */
+
+static void task_clock_perf_counter_update(struct perf_counter *counter, u64 now)
+{
+        u64 prev;
+        s64 delta;
+
+        prev = atomic64_xchg(&counter->hw.prev_count, now);
+        delta = now - prev;
+        atomic64_add(delta, &counter->count);
+}
+
+static int task_clock_perf_counter_enable(struct perf_counter *counter)
+{
+        struct hw_perf_counter *hwc = &counter->hw;
+        u64 now;
+
+        now = counter->ctx->time;
+
+        atomic64_set(&hwc->prev_count, now);
+        hrtimer_init(&hwc->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+        hwc->hrtimer.function = perf_swcounter_hrtimer;
+        if (hwc->sample_period) {
+                u64 period = max_t(u64, 10000, hwc->sample_period);
+                __hrtimer_start_range_ns(&hwc->hrtimer,
+                                ns_to_ktime(period), 0,
+                                HRTIMER_MODE_REL, 0);
+        }
+
+        return 0;
+}
+
+static void task_clock_perf_counter_disable(struct perf_counter *counter)
+{
+        if (counter->hw.sample_period)
+                hrtimer_cancel(&counter->hw.hrtimer);
+        task_clock_perf_counter_update(counter, counter->ctx->time);
+
+}
+
+static void task_clock_perf_counter_read(struct perf_counter *counter)
+{
+        u64 time;
+
+        if (!in_nmi()) {
+                update_context_time(counter->ctx);
+                time = counter->ctx->time;
+        } else {
+                u64 now = perf_clock();
+                u64 delta = now - counter->ctx->timestamp;
+                time = counter->ctx->time + delta;
+        }
+
+        task_clock_perf_counter_update(counter, time);
+}
+
+static const struct pmu perf_ops_task_clock = {
+        .enable         = task_clock_perf_counter_enable,
+        .disable        = task_clock_perf_counter_disable,
+        .read           = task_clock_perf_counter_read,
+};
+
+/*
+ * Software counter: cpu migrations
+ */
+void perf_counter_task_migration(struct task_struct *task, int cpu)
+{
+        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
+        struct perf_counter_context *ctx;
+
+        perf_swcounter_ctx_event(&cpuctx->ctx, PERF_TYPE_SOFTWARE,
+                                 PERF_COUNT_SW_CPU_MIGRATIONS,
+                                 1, 1, NULL, 0);
+
+        ctx = perf_pin_task_context(task);
+        if (ctx) {
+                perf_swcounter_ctx_event(ctx, PERF_TYPE_SOFTWARE,
+                                         PERF_COUNT_SW_CPU_MIGRATIONS,
+                                         1, 1, NULL, 0);
+                perf_unpin_context(ctx);
+        }
+}
+
+#ifdef CONFIG_EVENT_PROFILE
+void perf_tpcounter_event(int event_id)
+{
+        struct pt_regs *regs = get_irq_regs();
+
+        if (!regs)
+                regs = task_pt_regs(current);
+
+        __perf_swcounter_event(PERF_TYPE_TRACEPOINT, event_id, 1, 1, regs, 0);
+}
+EXPORT_SYMBOL_GPL(perf_tpcounter_event);
+
+extern int ftrace_profile_enable(int);
+extern void ftrace_profile_disable(int);
+
+static void tp_perf_counter_destroy(struct perf_counter *counter)
+{
+        ftrace_profile_disable(perf_event_id(&counter->attr));
+}
+
+static const struct pmu *tp_perf_counter_init(struct perf_counter *counter)
+{
+        int event_id = perf_event_id(&counter->attr);
+        int ret;
+
+        ret = ftrace_profile_enable(event_id);
+        if (ret)
+                return NULL;
+
+        counter->destroy = tp_perf_counter_destroy;
+
+        return &perf_ops_generic;
+}
+#else
+static const struct pmu *tp_perf_counter_init(struct perf_counter *counter)
+{
+        return NULL;
+}
+#endif
+
+static const struct pmu *sw_perf_counter_init(struct perf_counter *counter)
+{
+        const struct pmu *pmu = NULL;
+
+        /*
+         * Software counters (currently) can't in general distinguish
+         * between user, kernel and hypervisor events.
+         * However, context switches and cpu migrations are considered
+         * to be kernel events, and page faults are never hypervisor
+         * events.
+         */
+        switch (counter->attr.config) {
+        case PERF_COUNT_SW_CPU_CLOCK:
+                pmu = &perf_ops_cpu_clock;
+
+                break;
+        case PERF_COUNT_SW_TASK_CLOCK:
+                /*
+                 * If the user instantiates this as a per-cpu counter,
+                 * use the cpu_clock counter instead.
+                 */
+                if (counter->ctx->task)
+                        pmu = &perf_ops_task_clock;
+                else
+                        pmu = &perf_ops_cpu_clock;
+
+                break;
+        case PERF_COUNT_SW_PAGE_FAULTS:
+        case PERF_COUNT_SW_PAGE_FAULTS_MIN:
+        case PERF_COUNT_SW_PAGE_FAULTS_MAJ:
+        case PERF_COUNT_SW_CONTEXT_SWITCHES:
+        case PERF_COUNT_SW_CPU_MIGRATIONS:
+                pmu = &perf_ops_generic;
+                break;
+        }
+
+        return pmu;
+}
+
+/*
+ * Allocate and initialize a counter structure
+ */
+static struct perf_counter *
+perf_counter_alloc(struct perf_counter_attr *attr,
+                   int cpu,
+                   struct perf_counter_context *ctx,
+                   struct perf_counter *group_leader,
+                   gfp_t gfpflags)
+{
+        const struct pmu *pmu;
+        struct perf_counter *counter;
+        struct hw_perf_counter *hwc;
+        long err;
+
+        counter = kzalloc(sizeof(*counter), gfpflags);
+        if (!counter)
+                return ERR_PTR(-ENOMEM);
+
+        /*
+         * Single counters are their own group leaders, with an
+         * empty sibling list:
+         */
+        if (!group_leader)
+                group_leader = counter;
+
+        mutex_init(&counter->child_mutex);
+        INIT_LIST_HEAD(&counter->child_list);
+
+        INIT_LIST_HEAD(&counter->list_entry);
+        INIT_LIST_HEAD(&counter->event_entry);
+        INIT_LIST_HEAD(&counter->sibling_list);
+        init_waitqueue_head(&counter->waitq);
+
+        mutex_init(&counter->mmap_mutex);
+
+        counter->cpu            = cpu;
+        counter->attr           = *attr;
+        counter->group_leader   = group_leader;
+        counter->pmu            = NULL;
+        counter->ctx            = ctx;
+        counter->oncpu          = -1;
+
+        counter->ns             = get_pid_ns(current->nsproxy->pid_ns);
+        counter->id             = atomic64_inc_return(&perf_counter_id);
+
+        counter->state          = PERF_COUNTER_STATE_INACTIVE;
+
+        if (attr->disabled)
+                counter->state = PERF_COUNTER_STATE_OFF;
+
+        pmu = NULL;
+
+        hwc = &counter->hw;
+        hwc->sample_period = attr->sample_period;
+        if (attr->freq && attr->sample_freq)
+                hwc->sample_period = 1;
+
+        atomic64_set(&hwc->period_left, hwc->sample_period);
+
+        /*
+         * we currently do not support PERF_SAMPLE_GROUP on inherited counters
+         */
+        if (attr->inherit && (attr->sample_type & PERF_SAMPLE_GROUP))
+                goto done;
+
+        if (attr->type == PERF_TYPE_RAW) {
+                pmu = hw_perf_counter_init(counter);
+                goto done;
+        }
+
+        switch (attr->type) {
+        case PERF_TYPE_HARDWARE:
+        case PERF_TYPE_HW_CACHE:
+                pmu = hw_perf_counter_init(counter);
+                break;
+
+        case PERF_TYPE_SOFTWARE:
+                pmu = sw_perf_counter_init(counter);
+                break;
+
+        case PERF_TYPE_TRACEPOINT:
+                pmu = tp_perf_counter_init(counter);
+                break;
+        }
+done:
+        err = 0;
+        if (!pmu)
+                err = -EINVAL;
+        else if (IS_ERR(pmu))
+                err = PTR_ERR(pmu);
+
+        if (err) {
+                if (counter->ns)
+                        put_pid_ns(counter->ns);
+                kfree(counter);
+                return ERR_PTR(err);
+        }
+
+        counter->pmu = pmu;
+
+        atomic_inc(&nr_counters);
+        if (counter->attr.mmap)
+                atomic_inc(&nr_mmap_counters);
+        if (counter->attr.comm)
+                atomic_inc(&nr_comm_counters);
+
+        return counter;
+}
+
+/**
+ * sys_perf_counter_open - open a performance counter, associate it to a task/cpu
+ *
+ * @attr_uptr:  event type attributes for monitoring/sampling
+ * @pid:                target pid
+ * @cpu:                target cpu
+ * @group_fd:           group leader counter fd
+ */
+SYSCALL_DEFINE5(perf_counter_open,
+                const struct perf_counter_attr __user *, attr_uptr,
+                pid_t, pid, int, cpu, int, group_fd, unsigned long, flags)
+{
+        struct perf_counter *counter, *group_leader;
+        struct perf_counter_attr attr;
+        struct perf_counter_context *ctx;
+        struct file *counter_file = NULL;
+        struct file *group_file = NULL;
+        int fput_needed = 0;
+        int fput_needed2 = 0;
+        int ret;
+
+        /* for future expandability... */
+        if (flags)
+                return -EINVAL;
+
+        if (copy_from_user(&attr, attr_uptr, sizeof(attr)) != 0)
+                return -EFAULT;
+
+        if (!attr.exclude_kernel) {
+                if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
+                        return -EACCES;
+        }
+
+        if (attr.freq) {
+                if (attr.sample_freq > sysctl_perf_counter_sample_rate)
+                        return -EINVAL;
+        }
+
+        /*
+         * Get the target context (task or percpu):
+         */
+        ctx = find_get_context(pid, cpu);
+        if (IS_ERR(ctx))
+                return PTR_ERR(ctx);
+
+        /*
+         * Look up the group leader (we will attach this counter to it):
+         */
+        group_leader = NULL;
+        if (group_fd != -1) {
+                ret = -EINVAL;
+                group_file = fget_light(group_fd, &fput_needed);
+                if (!group_file)
+                        goto err_put_context;
+                if (group_file->f_op != &perf_fops)
+                        goto err_put_context;
+
+                group_leader = group_file->private_data;
+                /*
+                 * Do not allow a recursive hierarchy (this new sibling
+                 * becoming part of another group-sibling):
+                 */
+                if (group_leader->group_leader != group_leader)
+                        goto err_put_context;
+                /*
+                 * Do not allow to attach to a group in a different
+                 * task or CPU context:
+                 */
+                if (group_leader->ctx != ctx)
+                        goto err_put_context;
+                /*
+                 * Only a group leader can be exclusive or pinned
+                 */
+                if (attr.exclusive || attr.pinned)
+                        goto err_put_context;
+        }
+
+        counter = perf_counter_alloc(&attr, cpu, ctx, group_leader,
+                                     GFP_KERNEL);
+        ret = PTR_ERR(counter);
+        if (IS_ERR(counter))
+                goto err_put_context;
+
+        ret = anon_inode_getfd("[perf_counter]", &perf_fops, counter, 0);
+        if (ret < 0)
+                goto err_free_put_context;
+
+        counter_file = fget_light(ret, &fput_needed2);
+        if (!counter_file)
+                goto err_free_put_context;
+
+        counter->filp = counter_file;
+        WARN_ON_ONCE(ctx->parent_ctx);
+        mutex_lock(&ctx->mutex);
+        perf_install_in_context(ctx, counter, cpu);
+        ++ctx->generation;
+        mutex_unlock(&ctx->mutex);
+
+        counter->owner = current;
+        get_task_struct(current);
+        mutex_lock(&current->perf_counter_mutex);
+        list_add_tail(&counter->owner_entry, &current->perf_counter_list);
+        mutex_unlock(&current->perf_counter_mutex);
+
+        fput_light(counter_file, fput_needed2);
+
+out_fput:
+        fput_light(group_file, fput_needed);
+
+        return ret;
+
+err_free_put_context:
+        kfree(counter);
+
+err_put_context:
+        put_ctx(ctx);
+
+        goto out_fput;
+}
+
+/*
+ * inherit a counter from parent task to child task:
+ */
+static struct perf_counter *
+inherit_counter(struct perf_counter *parent_counter,
+              struct task_struct *parent,
+              struct perf_counter_context *parent_ctx,
+              struct task_struct *child,
+              struct perf_counter *group_leader,
+              struct perf_counter_context *child_ctx)
+{
+        struct perf_counter *child_counter;
+
+        /*
+         * Instead of creating recursive hierarchies of counters,
+         * we link inherited counters back to the original parent,
+         * which has a filp for sure, which we use as the reference
+         * count:
+         */
+        if (parent_counter->parent)
+                parent_counter = parent_counter->parent;
+
+        child_counter = perf_counter_alloc(&parent_counter->attr,
+                                           parent_counter->cpu, child_ctx,
+                                           group_leader, GFP_KERNEL);
+        if (IS_ERR(child_counter))
+                return child_counter;
+        get_ctx(child_ctx);
+
+        /*
+         * Make the child state follow the state of the parent counter,
+         * not its attr.disabled bit.  We hold the parent's mutex,
+         * so we won't race with perf_counter_{en, dis}able_family.
+         */
+        if (parent_counter->state >= PERF_COUNTER_STATE_INACTIVE)
+                child_counter->state = PERF_COUNTER_STATE_INACTIVE;
+        else
+                child_counter->state = PERF_COUNTER_STATE_OFF;
+
+        if (parent_counter->attr.freq)
+                child_counter->hw.sample_period = parent_counter->hw.sample_period;
+
+        /*
+         * Link it up in the child's context:
+         */
+        add_counter_to_ctx(child_counter, child_ctx);
+
+        child_counter->parent = parent_counter;
+        /*
+         * inherit into child's child as well:
+         */
+        child_counter->attr.inherit = 1;
+
+        /*
+         * Get a reference to the parent filp - we will fput it
+         * when the child counter exits. This is safe to do because
+         * we are in the parent and we know that the filp still
+         * exists and has a nonzero count:
+         */
+        atomic_long_inc(&parent_counter->filp->f_count);
+
+        /*
+         * Link this into the parent counter's child list
+         */
+        WARN_ON_ONCE(parent_counter->ctx->parent_ctx);
+        mutex_lock(&parent_counter->child_mutex);
+        list_add_tail(&child_counter->child_list, &parent_counter->child_list);
+        mutex_unlock(&parent_counter->child_mutex);
+
+        return child_counter;
+}
+
+static int inherit_group(struct perf_counter *parent_counter,
+              struct task_struct *parent,
+              struct perf_counter_context *parent_ctx,
+              struct task_struct *child,
+              struct perf_counter_context *child_ctx)
+{
+        struct perf_counter *leader;
+        struct perf_counter *sub;
+        struct perf_counter *child_ctr;
+
+        leader = inherit_counter(parent_counter, parent, parent_ctx,
+                                 child, NULL, child_ctx);
+        if (IS_ERR(leader))
+                return PTR_ERR(leader);
+        list_for_each_entry(sub, &parent_counter->sibling_list, list_entry) {
+                child_ctr = inherit_counter(sub, parent, parent_ctx,
+                                            child, leader, child_ctx);
+                if (IS_ERR(child_ctr))
+                        return PTR_ERR(child_ctr);
+        }
+        return 0;
+}
+
+static void sync_child_counter(struct perf_counter *child_counter,
+                               struct perf_counter *parent_counter)
+{
+        u64 child_val;
+
+        child_val = atomic64_read(&child_counter->count);
+
+        /*
+         * Add back the child's count to the parent's count:
+         */
+        atomic64_add(child_val, &parent_counter->count);
+        atomic64_add(child_counter->total_time_enabled,
+                     &parent_counter->child_total_time_enabled);
+        atomic64_add(child_counter->total_time_running,
+                     &parent_counter->child_total_time_running);
+
+        /*
+         * Remove this counter from the parent's list
+         */
+        WARN_ON_ONCE(parent_counter->ctx->parent_ctx);
+        mutex_lock(&parent_counter->child_mutex);
+        list_del_init(&child_counter->child_list);
+        mutex_unlock(&parent_counter->child_mutex);
+
+        /*
+         * Release the parent counter, if this was the last
+         * reference to it.
+         */
+        fput(parent_counter->filp);
+}
+
+static void
+__perf_counter_exit_task(struct perf_counter *child_counter,
+                         struct perf_counter_context *child_ctx)
+{
+        struct perf_counter *parent_counter;
+
+        update_counter_times(child_counter);
+        perf_counter_remove_from_context(child_counter);
+
+        parent_counter = child_counter->parent;
+        /*
+         * It can happen that parent exits first, and has counters
+         * that are still around due to the child reference. These
+         * counters need to be zapped - but otherwise linger.
+         */
+        if (parent_counter) {
+                sync_child_counter(child_counter, parent_counter);
+                free_counter(child_counter);
+        }
+}
+
+/*
+ * When a child task exits, feed back counter values to parent counters.
+ */
+void perf_counter_exit_task(struct task_struct *child)
+{
+        struct perf_counter *child_counter, *tmp;
+        struct perf_counter_context *child_ctx;
+        unsigned long flags;
+
+        if (likely(!child->perf_counter_ctxp))
+                return;
+
+        local_irq_save(flags);
+        /*
+         * We can't reschedule here because interrupts are disabled,
+         * and either child is current or it is a task that can't be
+         * scheduled, so we are now safe from rescheduling changing
+         * our context.
+         */
+        child_ctx = child->perf_counter_ctxp;
+        __perf_counter_task_sched_out(child_ctx);
+
+        /*
+         * Take the context lock here so that if find_get_context is
+         * reading child->perf_counter_ctxp, we wait until it has
+         * incremented the context's refcount before we do put_ctx below.
+         */
+        spin_lock(&child_ctx->lock);
+        child->perf_counter_ctxp = NULL;
+        if (child_ctx->parent_ctx) {
+                /*
+                 * This context is a clone; unclone it so it can't get
+                 * swapped to another process while we're removing all
+                 * the counters from it.
+                 */
+                put_ctx(child_ctx->parent_ctx);
+                child_ctx->parent_ctx = NULL;
+        }
+        spin_unlock(&child_ctx->lock);
+        local_irq_restore(flags);
+
+        /*
+         * We can recurse on the same lock type through:
+         *
+         *   __perf_counter_exit_task()
+         *     sync_child_counter()
+         *       fput(parent_counter->filp)
+         *         perf_release()
+         *           mutex_lock(&ctx->mutex)
+         *
+         * But since its the parent context it won't be the same instance.
+         */
+        mutex_lock_nested(&child_ctx->mutex, SINGLE_DEPTH_NESTING);
+
+again:
+        list_for_each_entry_safe(child_counter, tmp, &child_ctx->counter_list,
+                                 list_entry)
+                __perf_counter_exit_task(child_counter, child_ctx);
+
+        /*
+         * If the last counter was a group counter, it will have appended all
+         * its siblings to the list, but we obtained 'tmp' before that which
+         * will still point to the list head terminating the iteration.
+         */
+        if (!list_empty(&child_ctx->counter_list))
+                goto again;
+
+        mutex_unlock(&child_ctx->mutex);
+
+        put_ctx(child_ctx);
+}
+
+/*
+ * free an unexposed, unused context as created by inheritance by
+ * init_task below, used by fork() in case of fail.
+ */
+void perf_counter_free_task(struct task_struct *task)
+{
+        struct perf_counter_context *ctx = task->perf_counter_ctxp;
+        struct perf_counter *counter, *tmp;
+
+        if (!ctx)
+                return;
+
+        mutex_lock(&ctx->mutex);
+again:
+        list_for_each_entry_safe(counter, tmp, &ctx->counter_list, list_entry) {
+                struct perf_counter *parent = counter->parent;
+
+                if (WARN_ON_ONCE(!parent))
+                        continue;
+
+                mutex_lock(&parent->child_mutex);
+                list_del_init(&counter->child_list);
+                mutex_unlock(&parent->child_mutex);
+
+                fput(parent->filp);
+
+                list_del_counter(counter, ctx);
+                free_counter(counter);
+        }
+
+        if (!list_empty(&ctx->counter_list))
+                goto again;
+
+        mutex_unlock(&ctx->mutex);
+
+        put_ctx(ctx);
+}
+
+/*
+ * Initialize the perf_counter context in task_struct
+ */
+int perf_counter_init_task(struct task_struct *child)
+{
+        struct perf_counter_context *child_ctx, *parent_ctx;
+        struct perf_counter_context *cloned_ctx;
+        struct perf_counter *counter;
+        struct task_struct *parent = current;
+        int inherited_all = 1;
+        int ret = 0;
+
+        child->perf_counter_ctxp = NULL;
+
+        mutex_init(&child->perf_counter_mutex);
+        INIT_LIST_HEAD(&child->perf_counter_list);
+
+        if (likely(!parent->perf_counter_ctxp))
+                return 0;
+
+        /*
+         * This is executed from the parent task context, so inherit
+         * counters that have been marked for cloning.
+         * First allocate and initialize a context for the child.
+         */
+
+        child_ctx = kmalloc(sizeof(struct perf_counter_context), GFP_KERNEL);
+        if (!child_ctx)
+                return -ENOMEM;
+
+        __perf_counter_init_context(child_ctx, child);
+        child->perf_counter_ctxp = child_ctx;
+        get_task_struct(child);
+
+        /*
+         * If the parent's context is a clone, pin it so it won't get
+         * swapped under us.
+         */
+        parent_ctx = perf_pin_task_context(parent);
+
+        /*
+         * No need to check if parent_ctx != NULL here; since we saw
+         * it non-NULL earlier, the only reason for it to become NULL
+         * is if we exit, and since we're currently in the middle of
+         * a fork we can't be exiting at the same time.
+         */
+
+        /*
+         * Lock the parent list. No need to lock the child - not PID
+         * hashed yet and not running, so nobody can access it.
+         */
+        mutex_lock(&parent_ctx->mutex);
+
+        /*
+         * We dont have to disable NMIs - we are only looking at
+         * the list, not manipulating it:
+         */
+        list_for_each_entry_rcu(counter, &parent_ctx->event_list, event_entry) {
+                if (counter != counter->group_leader)
+                        continue;
+
+                if (!counter->attr.inherit) {
+                        inherited_all = 0;
+                        continue;
+                }
+
+                ret = inherit_group(counter, parent, parent_ctx,
+                                             child, child_ctx);
+                if (ret) {
+                        inherited_all = 0;
+                        break;
+                }
+        }
+
+        if (inherited_all) {
+                /*
+                 * Mark the child context as a clone of the parent
+                 * context, or of whatever the parent is a clone of.
+                 * Note that if the parent is a clone, it could get
+                 * uncloned at any point, but that doesn't matter
+                 * because the list of counters and the generation
+                 * count can't have changed since we took the mutex.
+                 */
+                cloned_ctx = rcu_dereference(parent_ctx->parent_ctx);
+                if (cloned_ctx) {
+                        child_ctx->parent_ctx = cloned_ctx;
+                        child_ctx->parent_gen = parent_ctx->parent_gen;
+                } else {
+                        child_ctx->parent_ctx = parent_ctx;
+                        child_ctx->parent_gen = parent_ctx->generation;
+                }
+                get_ctx(child_ctx->parent_ctx);
+        }
+
+        mutex_unlock(&parent_ctx->mutex);
+
+        perf_unpin_context(parent_ctx);
+
+        return ret;
+}
+
+static void __cpuinit perf_counter_init_cpu(int cpu)
+{
+        struct perf_cpu_context *cpuctx;
+
+        cpuctx = &per_cpu(perf_cpu_context, cpu);
+        __perf_counter_init_context(&cpuctx->ctx, NULL);
+
+        spin_lock(&perf_resource_lock);
+        cpuctx->max_pertask = perf_max_counters - perf_reserved_percpu;
+        spin_unlock(&perf_resource_lock);
+
+        hw_perf_counter_setup(cpu);
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+static void __perf_counter_exit_cpu(void *info)
+{
+        struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
+        struct perf_counter_context *ctx = &cpuctx->ctx;
+        struct perf_counter *counter, *tmp;
+
+        list_for_each_entry_safe(counter, tmp, &ctx->counter_list, list_entry)
+                __perf_counter_remove_from_context(counter);
+}
+static void perf_counter_exit_cpu(int cpu)
+{
+        struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);
+        struct perf_counter_context *ctx = &cpuctx->ctx;
+
+        mutex_lock(&ctx->mutex);
+        smp_call_function_single(cpu, __perf_counter_exit_cpu, NULL, 1);
+        mutex_unlock(&ctx->mutex);
+}
+#else
+static inline void perf_counter_exit_cpu(int cpu) { }
+#endif
+
+static int __cpuinit
+perf_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu)
+{
+        unsigned int cpu = (long)hcpu;
+
+        switch (action) {
+
+        case CPU_UP_PREPARE:
+        case CPU_UP_PREPARE_FROZEN:
+                perf_counter_init_cpu(cpu);
+                break;
+
+        case CPU_DOWN_PREPARE:
+        case CPU_DOWN_PREPARE_FROZEN:
+                perf_counter_exit_cpu(cpu);
+                break;
+
+        default:
+                break;
+        }
+
+        return NOTIFY_OK;
+}
+
+/*
+ * This has to have a higher priority than migration_notifier in sched.c.
+ */
+static struct notifier_block __cpuinitdata perf_cpu_nb = {
+        .notifier_call          = perf_cpu_notify,
+        .priority               = 20,
+};
+
+void __init perf_counter_init(void)
+{
+        perf_cpu_notify(&perf_cpu_nb, (unsigned long)CPU_UP_PREPARE,
+                        (void *)(long)smp_processor_id());
+        register_cpu_notifier(&perf_cpu_nb);
+}
+
+static ssize_t perf_show_reserve_percpu(struct sysdev_class *class, char *buf)
+{
+        return sprintf(buf, "%d\n", perf_reserved_percpu);
+}
+
+static ssize_t
+perf_set_reserve_percpu(struct sysdev_class *class,
+                        const char *buf,
+                        size_t count)
+{
+        struct perf_cpu_context *cpuctx;
+        unsigned long val;
+        int err, cpu, mpt;
+
+        err = strict_strtoul(buf, 10, &val);
+        if (err)
+                return err;
+        if (val > perf_max_counters)
+                return -EINVAL;
+
+        spin_lock(&perf_resource_lock);
+        perf_reserved_percpu = val;
+        for_each_online_cpu(cpu) {
+                cpuctx = &per_cpu(perf_cpu_context, cpu);
+                spin_lock_irq(&cpuctx->ctx.lock);
+                mpt = min(perf_max_counters - cpuctx->ctx.nr_counters,
+                          perf_max_counters - perf_reserved_percpu);
+                cpuctx->max_pertask = mpt;
+                spin_unlock_irq(&cpuctx->ctx.lock);
+        }
+        spin_unlock(&perf_resource_lock);
+
+        return count;
+}
+
+static ssize_t perf_show_overcommit(struct sysdev_class *class, char *buf)
+{
+        return sprintf(buf, "%d\n", perf_overcommit);
+}
+
+static ssize_t
+perf_set_overcommit(struct sysdev_class *class, const char *buf, size_t count)
+{
+        unsigned long val;
+        int err;
+
+        err = strict_strtoul(buf, 10, &val);
+        if (err)
+                return err;
+        if (val > 1)
+                return -EINVAL;
+
+        spin_lock(&perf_resource_lock);
+        perf_overcommit = val;
+        spin_unlock(&perf_resource_lock);
+
+        return count;
+}
+
+static SYSDEV_CLASS_ATTR(
+                                reserve_percpu,
+                                0644,
+                                perf_show_reserve_percpu,
+                                perf_set_reserve_percpu
+                        );
+
+static SYSDEV_CLASS_ATTR(
+                                overcommit,
+                                0644,
+                                perf_show_overcommit,
+                                perf_set_overcommit
+                        );
+
+static struct attribute *perfclass_attrs[] = {
+        &attr_reserve_percpu.attr,
+        &attr_overcommit.attr,
+        NULL
+};
+
+static struct attribute_group perfclass_attr_group = {
+        .attrs                  = perfclass_attrs,
+        .name                   = "perf_counters",
+};
+
+static int __init perf_counter_sysfs_init(void)
+{
+        return sysfs_create_group(&cpu_sysdev_class.kset.kobj,
+                                  &perfclass_attr_group);
+}
+device_initcall(perf_counter_sysfs_init);
diff --git a/kernel/sched.c b/kernel/sched.c
index dcf2dc28931a..f04aa9664504 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -39,6 +39,7 @@
 #include <linux/completion.h>
 #include <linux/kernel_stat.h>
 #include <linux/debug_locks.h>
+#include <linux/perf_counter.h>
 #include <linux/security.h>
 #include <linux/notifier.h>
 #include <linux/profile.h>
@@ -579,6 +580,7 @@ struct rq {
         struct load_weight load;
         unsigned long nr_load_updates;
         u64 nr_switches;
+        u64 nr_migrations_in;
 
         struct cfs_rq cfs;
         struct rt_rq rt;
@@ -691,7 +693,7 @@ static inline int cpu_of(struct rq *rq)
 #define task_rq(p)              cpu_rq(task_cpu(p))
 #define cpu_curr(cpu)           (cpu_rq(cpu)->curr)
 
-static inline void update_rq_clock(struct rq *rq)
+inline void update_rq_clock(struct rq *rq)
 {
         rq->clock = sched_clock_cpu(cpu_of(rq));
 }
@@ -1968,12 +1970,16 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
                 p->se.sleep_start -= clock_offset;
         if (p->se.block_start)
                 p->se.block_start -= clock_offset;
+#endif
         if (old_cpu != new_cpu) {
-                schedstat_inc(p, se.nr_migrations);
+                p->se.nr_migrations++;
+                new_rq->nr_migrations_in++;
+#ifdef CONFIG_SCHEDSTATS
                 if (task_hot(p, old_rq->clock, NULL))
                         schedstat_inc(p, se.nr_forced2_migrations);
-        }
 #endif
+                perf_counter_task_migration(p, new_cpu);
+        }
         p->se.vruntime -= old_cfsrq->min_vruntime -
                                          new_cfsrq->min_vruntime;
 
@@ -2368,6 +2374,27 @@ static int sched_balance_self(int cpu, int flag)
 
 #endif /* CONFIG_SMP */
 
+/**
+ * task_oncpu_function_call - call a function on the cpu on which a task runs
+ * @p:          the task to evaluate
+ * @func:       the function to be called
+ * @info:       the function call argument
+ *
+ * Calls the function @func when the task is currently running. This might
+ * be on the current CPU, which just calls the function directly
+ */
+void task_oncpu_function_call(struct task_struct *p,
+                              void (*func) (void *info), void *info)
+{
+        int cpu;
+
+        preempt_disable();
+        cpu = task_cpu(p);
+        if (task_curr(p))
+                smp_call_function_single(cpu, func, info, 1);
+        preempt_enable();
+}
+
 /***
  * try_to_wake_up - wake up a thread
  * @p: the to-be-woken-up thread
@@ -2535,6 +2562,7 @@ static void __sched_fork(struct task_struct *p)
         p->se.exec_start                = 0;
         p->se.sum_exec_runtime          = 0;
         p->se.prev_sum_exec_runtime     = 0;
+        p->se.nr_migrations             = 0;
         p->se.last_wakeup               = 0;
         p->se.avg_overlap               = 0;
         p->se.start_runtime             = 0;
@@ -2765,6 +2793,7 @@ static void finish_task_switch(struct rq *rq, struct task_struct *prev)
          */
         prev_state = prev->state;
         finish_arch_switch(prev);
+        perf_counter_task_sched_in(current, cpu_of(rq));
         finish_lock_switch(rq, prev);
 #ifdef CONFIG_SMP
         if (post_schedule)
@@ -2980,6 +3009,15 @@ static void calc_load_account_active(struct rq *this_rq)
 }
 
 /*
+ * Externally visible per-cpu scheduler statistics:
+ * cpu_nr_migrations(cpu) - number of migrations into that cpu
+ */
+u64 cpu_nr_migrations(int cpu)
+{
+        return cpu_rq(cpu)->nr_migrations_in;
+}
+
+/*
  * Update rq->cpu_load[] statistics. This function is usually called every
  * scheduler tick (TICK_NSEC).
  */
@@ -5077,6 +5115,8 @@ void scheduler_tick(void)
         curr->sched_class->task_tick(rq, curr, 0);
         spin_unlock(&rq->lock);
 
+        perf_counter_task_tick(curr, cpu);
+
 #ifdef CONFIG_SMP
         rq->idle_at_tick = idle_cpu(cpu);
         trigger_load_balance(rq, cpu);
@@ -5292,6 +5332,7 @@ need_resched_nonpreemptible:
 
         if (likely(prev != next)) {
                 sched_info_switch(prev, next);
+                perf_counter_task_sched_out(prev, next, cpu);
 
                 rq->nr_switches++;
                 rq->curr = next;
@@ -7535,8 +7576,10 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
         return NOTIFY_OK;
 }
 
-/* Register at highest priority so that task migration (migrate_all_tasks)
- * happens before everything else.
+/*
+ * Register at high priority so that task migration (migrate_all_tasks)
+ * happens before everything else.  This has to be lower priority than
+ * the notifier in the perf_counter subsystem, though.
  */
 static struct notifier_block __cpuinitdata migration_notifier = {
         .notifier_call = migration_call,
@@ -9214,7 +9257,7 @@ void __init sched_init(void)
                  * 1024) and two child groups A0 and A1 (of weight 1024 each),
                  * then A0's share of the cpu resource is:
                  *
-                 *      A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33%
+                 *      A0's bandwidth = 1024 / (10*1024 + 1024 + 1024) = 8.33%
                  *
                  * We achieve this by letting init_task_group's tasks sit
                  * directly in rq->cfs (i.e init_task_group->se[] = NULL).
@@ -9319,6 +9362,8 @@ void __init sched_init(void)
         alloc_cpumask_var(&cpu_isolated_map, GFP_NOWAIT);
 #endif /* SMP */
 
+        perf_counter_init();
+
         scheduler_running = 1;
 }
 
diff --git a/kernel/sys.c b/kernel/sys.c
index e7998cf31498..438d99a38c87 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -14,6 +14,7 @@
 #include <linux/prctl.h>
 #include <linux/highuid.h>
 #include <linux/fs.h>
+#include <linux/perf_counter.h>
 #include <linux/resource.h>
 #include <linux/kernel.h>
 #include <linux/kexec.h>
@@ -1793,6 +1794,12 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
                 case PR_SET_TSC:
                         error = SET_TSC_CTL(arg2);
                         break;
+                case PR_TASK_PERF_COUNTERS_DISABLE:
+                        error = perf_counter_task_disable();
+                        break;
+                case PR_TASK_PERF_COUNTERS_ENABLE:
+                        error = perf_counter_task_enable();
+                        break;
                 case PR_GET_TIMERSLACK:
                         error = current->timer_slack_ns;
                         break;
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 27dad2967387..68320f6b07b5 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -175,3 +175,6 @@ cond_syscall(compat_sys_timerfd_settime);
 cond_syscall(compat_sys_timerfd_gettime);
 cond_syscall(sys_eventfd);
 cond_syscall(sys_eventfd2);
+
+/* performance counters: */
+cond_syscall(sys_perf_counter_open);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 944ba03cae19..ce664f98e3fb 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -49,6 +49,7 @@
 #include <linux/reboot.h>
 #include <linux/ftrace.h>
 #include <linux/slow-work.h>
+#include <linux/perf_counter.h>
 
 #include <asm/uaccess.h>
 #include <asm/processor.h>
@@ -932,6 +933,32 @@ static struct ctl_table kern_table[] = {
                 .child          = slow_work_sysctls,
         },
 #endif
+#ifdef CONFIG_PERF_COUNTERS
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "perf_counter_paranoid",
+                .data           = &sysctl_perf_counter_paranoid,
+                .maxlen         = sizeof(sysctl_perf_counter_paranoid),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "perf_counter_mlock_kb",
+                .data           = &sysctl_perf_counter_mlock,
+                .maxlen         = sizeof(sysctl_perf_counter_mlock),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "perf_counter_max_sample_rate",
+                .data           = &sysctl_perf_counter_sample_rate,
+                .maxlen         = sizeof(sysctl_perf_counter_sample_rate),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+#endif
 /*
  * NOTE: do not add new entries to this table unless you have read
  * Documentation/sysctl/ctl_unnumbered.txt
diff --git a/kernel/timer.c b/kernel/timer.c
index a26ed294f938..c01e568935ea 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -37,6 +37,7 @@
 #include <linux/delay.h>
 #include <linux/tick.h>
 #include <linux/kallsyms.h>
+#include <linux/perf_counter.h>
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
@@ -1129,6 +1130,8 @@ static void run_timer_softirq(struct softirq_action *h)
 {
         struct tvec_base *base = __get_cpu_var(tvec_bases);
 
+        perf_counter_do_pending();
+
         hrtimer_run_pending();
 
         if (time_after_eq(jiffies, base->timer_jiffies))