8 files changed, 348 insertions, 12 deletions

diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index b0b814d75ca1..60740e8ecb37 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -836,7 +836,6 @@ Provides counts of softirq handlers serviced since boot time, for each cpu.
  TASKLET:          0          0          0        290
    SCHED:      27035      26983      26971      26746
  HRTIMER:          0          0          0          0
-     RCU:       1678       1769       2178       2250
 
 
 1.3 IDE devices in /proc/ide
diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index bea0ac750712..6c12989839d9 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -414,7 +414,6 @@ enum
         TASKLET_SOFTIRQ,
         SCHED_SOFTIRQ,
         HRTIMER_SOFTIRQ,
-        RCU_SOFTIRQ,    /* Preferable RCU should always be the last softirq */
 
         NR_SOFTIRQS
 };
diff --git a/include/trace/events/irq.h b/include/trace/events/irq.h
index 1c09820df585..ae045ca7d356 100644
--- a/include/trace/events/irq.h
+++ b/include/trace/events/irq.h
@@ -20,8 +20,7 @@ struct softirq_action;
                          softirq_name(BLOCK_IOPOLL),    \
                          softirq_name(TASKLET),         \
                          softirq_name(SCHED),           \
-                         softirq_name(HRTIMER),         \
-                         softirq_name(RCU))
+                         softirq_name(HRTIMER))
 
 /**
  * irq_handler_entry - called immediately before the irq action handler
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0ac1cc03f935..18e33313873e 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -47,6 +47,8 @@
 #include <linux/mutex.h>
 #include <linux/time.h>
 #include <linux/kernel_stat.h>
+#include <linux/wait.h>
+#include <linux/kthread.h>
 
 #include "rcutree.h"
 
@@ -83,6 +85,20 @@ int rcu_scheduler_active __read_mostly;
 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
 
 /*
+ * Control variables for per-CPU and per-rcu_node kthreads.  These
+ * handle all flavors of RCU.
+ */
+static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
+static DEFINE_PER_CPU(wait_queue_head_t, rcu_cpu_wq);
+static DEFINE_PER_CPU(char, rcu_cpu_has_work);
+static char rcu_kthreads_spawnable;
+
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp);
+static void invoke_rcu_kthread(void);
+
+#define RCU_KTHREAD_PRIO 1      /* RT priority for per-CPU kthreads. */
+
+/*
  * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
  * permit this function to be invoked without holding the root rcu_node
  * structure's ->lock, but of course results can be subject to change.
@@ -1009,6 +1025,8 @@ static void rcu_send_cbs_to_online(struct rcu_state *rsp)
 /*
  * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
  * and move all callbacks from the outgoing CPU to the current one.
+ * There can only be one CPU hotplug operation at a time, so no other
+ * CPU can be attempting to update rcu_cpu_kthread_task.
  */
 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
 {
@@ -1017,6 +1035,14 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
         int need_report = 0;
         struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
         struct rcu_node *rnp;
+        struct task_struct *t;
+
+        /* Stop the CPU's kthread. */
+        t = per_cpu(rcu_cpu_kthread_task, cpu);
+        if (t != NULL) {
+                per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
+                kthread_stop(t);
+        }
 
         /* Exclude any attempts to start a new grace period. */
         raw_spin_lock_irqsave(&rsp->onofflock, flags);
@@ -1054,6 +1080,19 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
                 raw_spin_unlock_irqrestore(&rnp->lock, flags);
         if (need_report & RCU_OFL_TASKS_EXP_GP)
                 rcu_report_exp_rnp(rsp, rnp);
+
+        /*
+         * If there are no more online CPUs for this rcu_node structure,
+         * kill the rcu_node structure's kthread.  Otherwise, adjust its
+         * affinity.
+         */
+        t = rnp->node_kthread_task;
+        if (t != NULL &&
+            rnp->qsmaskinit == 0) {
+                kthread_stop(t);
+                rnp->node_kthread_task = NULL;
+        } else
+                rcu_node_kthread_setaffinity(rnp);
 }
 
 /*
@@ -1151,7 +1190,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
 
         /* Re-raise the RCU softirq if there are callbacks remaining. */
         if (cpu_has_callbacks_ready_to_invoke(rdp))
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_kthread();
 }
 
 /*
@@ -1197,7 +1236,7 @@ void rcu_check_callbacks(int cpu, int user)
         }
         rcu_preempt_check_callbacks(cpu);
         if (rcu_pending(cpu))
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_kthread();
 }
 
 #ifdef CONFIG_SMP
@@ -1361,7 +1400,7 @@ __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
 /*
  * Do softirq processing for the current CPU.
  */
-static void rcu_process_callbacks(struct softirq_action *unused)
+static void rcu_process_callbacks(void)
 {
         __rcu_process_callbacks(&rcu_sched_state,
                                 &__get_cpu_var(rcu_sched_data));
@@ -1372,6 +1411,281 @@ static void rcu_process_callbacks(struct softirq_action *unused)
         rcu_needs_cpu_flush();
 }
 
+/*
+ * Wake up the current CPU's kthread.  This replaces raise_softirq()
+ * in earlier versions of RCU.  Note that because we are running on
+ * the current CPU with interrupts disabled, the rcu_cpu_kthread_task
+ * cannot disappear out from under us.
+ */
+static void invoke_rcu_kthread(void)
+{
+        unsigned long flags;
+        wait_queue_head_t *q;
+        int cpu;
+
+        local_irq_save(flags);
+        cpu = smp_processor_id();
+        per_cpu(rcu_cpu_has_work, cpu) = 1;
+        if (per_cpu(rcu_cpu_kthread_task, cpu) == NULL) {
+                local_irq_restore(flags);
+                return;
+        }
+        q = &per_cpu(rcu_cpu_wq, cpu);
+        wake_up(q);
+        local_irq_restore(flags);
+}
+
+/*
+ * Timer handler to initiate the waking up of per-CPU kthreads that
+ * have yielded the CPU due to excess numbers of RCU callbacks.
+ */
+static void rcu_cpu_kthread_timer(unsigned long arg)
+{
+        unsigned long flags;
+        struct rcu_data *rdp = (struct rcu_data *)arg;
+        struct rcu_node *rnp = rdp->mynode;
+        struct task_struct *t;
+
+        raw_spin_lock_irqsave(&rnp->lock, flags);
+        rnp->wakemask |= rdp->grpmask;
+        t = rnp->node_kthread_task;
+        if (t == NULL) {
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                return;
+        }
+        wake_up_process(t);
+        raw_spin_unlock_irqrestore(&rnp->lock, flags);
+}
+
+/*
+ * Drop to non-real-time priority and yield, but only after posting a
+ * timer that will cause us to regain our real-time priority if we
+ * remain preempted.  Either way, we restore our real-time priority
+ * before returning.
+ */
+static void rcu_yield(int cpu)
+{
+        struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
+        struct sched_param sp;
+        struct timer_list yield_timer;
+
+        setup_timer_on_stack(&yield_timer, rcu_cpu_kthread_timer, (unsigned long)rdp);
+        mod_timer(&yield_timer, jiffies + 2);
+        sp.sched_priority = 0;
+        sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
+        schedule();
+        sp.sched_priority = RCU_KTHREAD_PRIO;
+        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
+        del_timer(&yield_timer);
+}
+
+/*
+ * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
+ * This can happen while the corresponding CPU is either coming online
+ * or going offline.  We cannot wait until the CPU is fully online
+ * before starting the kthread, because the various notifier functions
+ * can wait for RCU grace periods.  So we park rcu_cpu_kthread() until
+ * the corresponding CPU is online.
+ *
+ * Return 1 if the kthread needs to stop, 0 otherwise.
+ *
+ * Caller must disable bh.  This function can momentarily enable it.
+ */
+static int rcu_cpu_kthread_should_stop(int cpu)
+{
+        while (cpu_is_offline(cpu) ||
+               !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
+               smp_processor_id() != cpu) {
+                if (kthread_should_stop())
+                        return 1;
+                local_bh_enable();
+                schedule_timeout_uninterruptible(1);
+                if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
+                        set_cpus_allowed_ptr(current, cpumask_of(cpu));
+                local_bh_disable();
+        }
+        return 0;
+}
+
+/*
+ * Per-CPU kernel thread that invokes RCU callbacks.  This replaces the
+ * earlier RCU softirq.
+ */
+static int rcu_cpu_kthread(void *arg)
+{
+        int cpu = (int)(long)arg;
+        unsigned long flags;
+        int spincnt = 0;
+        wait_queue_head_t *wqp = &per_cpu(rcu_cpu_wq, cpu);
+        char work;
+        char *workp = &per_cpu(rcu_cpu_has_work, cpu);
+
+        for (;;) {
+                wait_event_interruptible(*wqp,
+                                         *workp != 0 || kthread_should_stop());
+                local_bh_disable();
+                if (rcu_cpu_kthread_should_stop(cpu)) {
+                        local_bh_enable();
+                        break;
+                }
+                local_irq_save(flags);
+                work = *workp;
+                *workp = 0;
+                local_irq_restore(flags);
+                if (work)
+                        rcu_process_callbacks();
+                local_bh_enable();
+                if (*workp != 0)
+                        spincnt++;
+                else
+                        spincnt = 0;
+                if (spincnt > 10) {
+                        rcu_yield(cpu);
+                        spincnt = 0;
+                }
+        }
+        return 0;
+}
+
+/*
+ * Spawn a per-CPU kthread, setting up affinity and priority.
+ * Because the CPU hotplug lock is held, no other CPU will be attempting
+ * to manipulate rcu_cpu_kthread_task.  There might be another CPU
+ * attempting to access it during boot, but the locking in kthread_bind()
+ * will enforce sufficient ordering.
+ */
+static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
+{
+        struct sched_param sp;
+        struct task_struct *t;
+
+        if (!rcu_kthreads_spawnable ||
+            per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
+                return 0;
+        t = kthread_create(rcu_cpu_kthread, (void *)(long)cpu, "rcuc%d", cpu);
+        if (IS_ERR(t))
+                return PTR_ERR(t);
+        kthread_bind(t, cpu);
+        WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
+        per_cpu(rcu_cpu_kthread_task, cpu) = t;
+        wake_up_process(t);
+        sp.sched_priority = RCU_KTHREAD_PRIO;
+        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+        return 0;
+}
+
+/*
+ * Per-rcu_node kthread, which is in charge of waking up the per-CPU
+ * kthreads when needed.  We ignore requests to wake up kthreads
+ * for offline CPUs, which is OK because force_quiescent_state()
+ * takes care of this case.
+ */
+static int rcu_node_kthread(void *arg)
+{
+        int cpu;
+        unsigned long flags;
+        unsigned long mask;
+        struct rcu_node *rnp = (struct rcu_node *)arg;
+        struct sched_param sp;
+        struct task_struct *t;
+
+        for (;;) {
+                wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
+                                                       kthread_should_stop());
+                if (kthread_should_stop())
+                        break;
+                raw_spin_lock_irqsave(&rnp->lock, flags);
+                mask = rnp->wakemask;
+                rnp->wakemask = 0;
+                raw_spin_unlock_irqrestore(&rnp->lock, flags);
+                for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
+                        if ((mask & 0x1) == 0)
+                                continue;
+                        preempt_disable();
+                        t = per_cpu(rcu_cpu_kthread_task, cpu);
+                        if (!cpu_online(cpu) || t == NULL) {
+                                preempt_enable();
+                                continue;
+                        }
+                        per_cpu(rcu_cpu_has_work, cpu) = 1;
+                        sp.sched_priority = RCU_KTHREAD_PRIO;
+                        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+                        preempt_enable();
+                }
+        }
+        return 0;
+}
+
+/*
+ * Set the per-rcu_node kthread's affinity to cover all CPUs that are
+ * served by the rcu_node in question.
+ */
+static void rcu_node_kthread_setaffinity(struct rcu_node *rnp)
+{
+        cpumask_var_t cm;
+        int cpu;
+        unsigned long mask = rnp->qsmaskinit;
+
+        if (rnp->node_kthread_task == NULL ||
+            rnp->qsmaskinit == 0)
+                return;
+        if (!alloc_cpumask_var(&cm, GFP_KERNEL))
+                return;
+        cpumask_clear(cm);
+        for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
+                if (mask & 0x1)
+                        cpumask_set_cpu(cpu, cm);
+        set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
+        free_cpumask_var(cm);
+}
+
+/*
+ * Spawn a per-rcu_node kthread, setting priority and affinity.
+ */
+static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
+                                                struct rcu_node *rnp)
+{
+        int rnp_index = rnp - &rsp->node[0];
+        struct sched_param sp;
+        struct task_struct *t;
+
+        if (!rcu_kthreads_spawnable ||
+            rnp->qsmaskinit == 0 ||
+            rnp->node_kthread_task != NULL)
+                return 0;
+        t = kthread_create(rcu_node_kthread, (void *)rnp, "rcun%d", rnp_index);
+        if (IS_ERR(t))
+                return PTR_ERR(t);
+        rnp->node_kthread_task = t;
+        wake_up_process(t);
+        sp.sched_priority = 99;
+        sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
+        return 0;
+}
+
+/*
+ * Spawn all kthreads -- called as soon as the scheduler is running.
+ */
+static int __init rcu_spawn_kthreads(void)
+{
+        int cpu;
+        struct rcu_node *rnp;
+
+        rcu_kthreads_spawnable = 1;
+        for_each_possible_cpu(cpu) {
+                init_waitqueue_head(&per_cpu(rcu_cpu_wq, cpu));
+                per_cpu(rcu_cpu_has_work, cpu) = 0;
+                if (cpu_online(cpu))
+                        (void)rcu_spawn_one_cpu_kthread(cpu);
+        }
+        rcu_for_each_leaf_node(&rcu_sched_state, rnp) {
+                init_waitqueue_head(&rnp->node_wq);
+                (void)rcu_spawn_one_node_kthread(&rcu_sched_state, rnp);
+        }
+        return 0;
+}
+early_initcall(rcu_spawn_kthreads);
+
 static void
 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
            struct rcu_state *rsp)
@@ -1771,6 +2085,19 @@ static void __cpuinit rcu_online_cpu(int cpu)
         rcu_preempt_init_percpu_data(cpu);
 }
 
+static void __cpuinit rcu_online_kthreads(int cpu)
+{
+        struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
+        struct rcu_node *rnp = rdp->mynode;
+
+        /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
+        if (rcu_kthreads_spawnable) {
+                (void)rcu_spawn_one_cpu_kthread(cpu);
+                if (rnp->node_kthread_task == NULL)
+                        (void)rcu_spawn_one_node_kthread(&rcu_sched_state, rnp);
+        }
+}
+
 /*
  * Handle CPU online/offline notification events.
  */
@@ -1778,11 +2105,17 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
                                     unsigned long action, void *hcpu)
 {
         long cpu = (long)hcpu;
+        struct rcu_data *rdp = per_cpu_ptr(rcu_sched_state.rda, cpu);
+        struct rcu_node *rnp = rdp->mynode;
 
         switch (action) {
         case CPU_UP_PREPARE:
         case CPU_UP_PREPARE_FROZEN:
                 rcu_online_cpu(cpu);
+                rcu_online_kthreads(cpu);
+                break;
+        case CPU_ONLINE:
+                rcu_node_kthread_setaffinity(rnp);
                 break;
         case CPU_DYING:
         case CPU_DYING_FROZEN:
@@ -1923,7 +2256,6 @@ void __init rcu_init(void)
         rcu_init_one(&rcu_sched_state, &rcu_sched_data);
         rcu_init_one(&rcu_bh_state, &rcu_bh_data);
         __rcu_init_preempt();
-        open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
 
         /*
          * We don't need protection against CPU-hotplug here because
diff --git a/kernel/rcutree.h b/kernel/rcutree.h
index 5a439c180e69..c0213802d164 100644
--- a/kernel/rcutree.h
+++ b/kernel/rcutree.h
@@ -111,6 +111,7 @@ struct rcu_node {
                                 /*  elements that need to drain to allow the */
                                 /*  current expedited grace period to */
                                 /*  complete (only for TREE_PREEMPT_RCU). */
+        unsigned long wakemask; /* CPUs whose kthread needs to be awakened. */
         unsigned long qsmaskinit;
                                 /* Per-GP initial value for qsmask & expmask. */
         unsigned long grpmask;  /* Mask to apply to parent qsmask. */
@@ -134,6 +135,13 @@ struct rcu_node {
                                 /*  if there is no such task.  If there */
                                 /*  is no current expedited grace period, */
                                 /*  then there can cannot be any such task. */
+        struct task_struct *node_kthread_task;
+                                /* kthread that takes care of this rcu_node */
+                                /*  structure, for example, awakening the */
+                                /*  per-CPU kthreads as needed. */
+        wait_queue_head_t node_wq;
+                                /* Wait queue on which to park the per-node */
+                                /*  kthread. */
 } ____cacheline_internodealigned_in_smp;
 
 /*
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 774f010a4619..b9bd69a5a4fe 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -1206,7 +1206,7 @@ static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
  *
  * Because it is not legal to invoke rcu_process_callbacks() with irqs
  * disabled, we do one pass of force_quiescent_state(), then do a
- * raise_softirq() to cause rcu_process_callbacks() to be invoked later.
+ * invoke_rcu_kthread() to cause rcu_process_callbacks() to be invoked later.
  * The per-cpu rcu_dyntick_drain variable controls the sequencing.
  */
 int rcu_needs_cpu(int cpu)
@@ -1257,7 +1257,7 @@ int rcu_needs_cpu(int cpu)
 
         /* If RCU callbacks are still pending, RCU still needs this CPU. */
         if (c)
-                raise_softirq(RCU_SOFTIRQ);
+                invoke_rcu_kthread();
         return c;
 }
 
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 174f976c2874..13960170cad4 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -58,7 +58,7 @@ DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
 
 char *softirq_to_name[NR_SOFTIRQS] = {
         "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
-        "TASKLET", "SCHED", "HRTIMER",  "RCU"
+        "TASKLET", "SCHED", "HRTIMER"
 };
 
 /*
diff --git a/tools/perf/util/trace-event-parse.c b/tools/perf/util/trace-event-parse.c
index 0a7ed5b5e281..1e88485c16a0 100644
--- a/tools/perf/util/trace-event-parse.c
+++ b/tools/perf/util/trace-event-parse.c
@@ -2187,7 +2187,6 @@ static const struct flag flags[] = {
         { "TASKLET_SOFTIRQ", 6 },
         { "SCHED_SOFTIRQ", 7 },
         { "HRTIMER_SOFTIRQ", 8 },
-        { "RCU_SOFTIRQ", 9 },
 
         { "HRTIMER_NORESTART", 0 },
         { "HRTIMER_RESTART", 1 },