perf_counter: Full task tracing

In order to be able to distinguish between no samples due to
inactivity and no samples due to task ended, Arjan asked for
PERF_EVENT_EXIT events. This is useful to the boot delay
instrumentation (bootchart) app.

This patch changes the PERF_EVENT_FORK to be emitted on every
clone, and adds PERF_EVENT_EXIT to be emitted on task exit,
after the task's counters have been closed.

This task tracing is controlled through: attr.comm || attr.mmap
and through the new attr.task field.

Suggested-by: Arjan van de Ven <arjan@linux.intel.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Anton Blanchard <anton@samba.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
[ cleaned up perf_counter.h a bit ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 59 insertions, 32 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 29b532e718f7..466531eb92cc 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1269,6 +1269,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
         write_unlock_irq(&tasklist_lock);
         proc_fork_connector(p);
         cgroup_post_fork(p);
+        perf_counter_fork(p);
         return p;
 
 bad_fork_free_pid:
@@ -1410,9 +1411,6 @@ long do_fork(unsigned long clone_flags,
                         init_completion(&vfork);
                 }
 
-                if (!(clone_flags & CLONE_THREAD))
-                        perf_counter_fork(p);
-
                 audit_finish_fork(p);
                 tracehook_report_clone(regs, clone_flags, nr, p);
 
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 48471d75ae01..199ed4771315 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -42,6 +42,7 @@ 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;
+static atomic_t nr_task_counters __read_mostly;
 
 /*
  * perf counter paranoia level:
@@ -1654,6 +1655,8 @@ static void free_counter(struct perf_counter *counter)
                         atomic_dec(&nr_mmap_counters);
                 if (counter->attr.comm)
                         atomic_dec(&nr_comm_counters);
+                if (counter->attr.task)
+                        atomic_dec(&nr_task_counters);
         }
 
         if (counter->destroy)
@@ -2831,10 +2834,12 @@ perf_counter_read_event(struct perf_counter *counter,
 }
 
 /*
- * fork tracking
+ * task tracking -- fork/exit
+ *
+ * enabled by: attr.comm | attr.mmap | attr.task
  */
 
-struct perf_fork_event {
+struct perf_task_event {
         struct task_struct      *task;
 
         struct {
@@ -2842,37 +2847,42 @@ struct perf_fork_event {
 
                 u32                             pid;
                 u32                             ppid;
+                u32                             tid;
+                u32                             ptid;
         } event;
 };
 
-static void perf_counter_fork_output(struct perf_counter *counter,
-                                     struct perf_fork_event *fork_event)
+static void perf_counter_task_output(struct perf_counter *counter,
+                                     struct perf_task_event *task_event)
 {
         struct perf_output_handle handle;
-        int size = fork_event->event.header.size;
-        struct task_struct *task = fork_event->task;
+        int size = task_event->event.header.size;
+        struct task_struct *task = task_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);
+        task_event->event.pid = perf_counter_pid(counter, task);
+        task_event->event.ppid = perf_counter_pid(counter, task->real_parent);
 
-        perf_output_put(&handle, fork_event->event);
+        task_event->event.tid = perf_counter_tid(counter, task);
+        task_event->event.ptid = perf_counter_tid(counter, task->real_parent);
+
+        perf_output_put(&handle, task_event->event);
         perf_output_end(&handle);
 }
 
-static int perf_counter_fork_match(struct perf_counter *counter)
+static int perf_counter_task_match(struct perf_counter *counter)
 {
-        if (counter->attr.comm || counter->attr.mmap)
+        if (counter->attr.comm || counter->attr.mmap || counter->attr.task)
                 return 1;
 
         return 0;
 }
 
-static void perf_counter_fork_ctx(struct perf_counter_context *ctx,
-                                  struct perf_fork_event *fork_event)
+static void perf_counter_task_ctx(struct perf_counter_context *ctx,
+                                  struct perf_task_event *task_event)
 {
         struct perf_counter *counter;
 
@@ -2881,19 +2891,19 @@ static void perf_counter_fork_ctx(struct perf_counter_context *ctx,
 
         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);
+                if (perf_counter_task_match(counter))
+                        perf_counter_task_output(counter, task_event);
         }
         rcu_read_unlock();
 }
 
-static void perf_counter_fork_event(struct perf_fork_event *fork_event)
+static void perf_counter_task_event(struct perf_task_event *task_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);
+        perf_counter_task_ctx(&cpuctx->ctx, task_event);
         put_cpu_var(perf_cpu_context);
 
         rcu_read_lock();
@@ -2903,32 +2913,40 @@ static void perf_counter_fork_event(struct perf_fork_event *fork_event)
          */
         ctx = rcu_dereference(current->perf_counter_ctxp);
         if (ctx)
-                perf_counter_fork_ctx(ctx, fork_event);
+                perf_counter_task_ctx(ctx, task_event);
         rcu_read_unlock();
 }
 
-void perf_counter_fork(struct task_struct *task)
+static void perf_counter_task(struct task_struct *task, int new)
 {
-        struct perf_fork_event fork_event;
+        struct perf_task_event task_event;
 
         if (!atomic_read(&nr_comm_counters) &&
-            !atomic_read(&nr_mmap_counters))
+            !atomic_read(&nr_mmap_counters) &&
+            !atomic_read(&nr_task_counters))
                 return;
 
-        fork_event = (struct perf_fork_event){
+        task_event = (struct perf_task_event){
                 .task   = task,
                 .event  = {
                         .header = {
-                                .type = PERF_EVENT_FORK,
+                                .type = new ? PERF_EVENT_FORK : PERF_EVENT_EXIT,
                                 .misc = 0,
-                                .size = sizeof(fork_event.event),
+                                .size = sizeof(task_event.event),
                         },
                         /* .pid  */
                         /* .ppid */
+                        /* .tid  */
+                        /* .ptid */
                 },
         };
 
-        perf_counter_fork_event(&fork_event);
+        perf_counter_task_event(&task_event);
+}
+
+void perf_counter_fork(struct task_struct *task)
+{
+        perf_counter_task(task, 1);
 }
 
 /*
@@ -3887,6 +3905,8 @@ done:
                         atomic_inc(&nr_mmap_counters);
                 if (counter->attr.comm)
                         atomic_inc(&nr_comm_counters);
+                if (counter->attr.task)
+                        atomic_inc(&nr_task_counters);
         }
 
         return counter;
@@ -4248,8 +4268,10 @@ void perf_counter_exit_task(struct task_struct *child)
         struct perf_counter_context *child_ctx;
         unsigned long flags;
 
-        if (likely(!child->perf_counter_ctxp))
+        if (likely(!child->perf_counter_ctxp)) {
+                perf_counter_task(child, 0);
                 return;
+        }
 
         local_irq_save(flags);
         /*
@@ -4267,15 +4289,22 @@ void perf_counter_exit_task(struct task_struct *child)
          * incremented the context's refcount before we do put_ctx below.
          */
         spin_lock(&child_ctx->lock);
-        child->perf_counter_ctxp = NULL;
         /*
          * If 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.
          */
         unclone_ctx(child_ctx);
-        spin_unlock(&child_ctx->lock);
-        local_irq_restore(flags);
+        spin_unlock_irqrestore(&child_ctx->lock, flags);
+
+        /*
+         * Report the task dead after unscheduling the counters so that we
+         * won't get any samples after PERF_EVENT_EXIT. We can however still
+         * get a few PERF_EVENT_READ events.
+         */
+        perf_counter_task(child, 0);
+
+        child->perf_counter_ctxp = NULL;
 
         /*
          * We can recurse on the same lock type through: