tracing: Adjust conditional expression latency formatting.
[linux-2.6.git] / kernel / rcutiny.c
index 9f6d9ff..0c343b9 100644 (file)
 #include <linux/time.h>
 #include <linux/cpu.h>
 
-/* Global control variables for rcupdate callback mechanism. */
-struct rcu_ctrlblk {
-       struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
-       struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
-       struct rcu_head **curtail;      /* ->next pointer of last CB. */
-};
-
-/* Definition for rcupdate control block. */
-static struct rcu_ctrlblk rcu_ctrlblk = {
-       .donetail       = &rcu_ctrlblk.rcucblist,
-       .curtail        = &rcu_ctrlblk.rcucblist,
-};
-
-static struct rcu_ctrlblk rcu_bh_ctrlblk = {
-       .donetail       = &rcu_bh_ctrlblk.rcucblist,
-       .curtail        = &rcu_bh_ctrlblk.rcucblist,
-};
+/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
+static struct task_struct *rcu_kthread_task;
+static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
+static unsigned long have_rcu_kthread_work;
+static void invoke_rcu_kthread(void);
+
+/* Forward declarations for rcutiny_plugin.h. */
+struct rcu_ctrlblk;
+static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
+static int rcu_kthread(void *arg);
+static void __call_rcu(struct rcu_head *head,
+                      void (*func)(struct rcu_head *rcu),
+                      struct rcu_ctrlblk *rcp);
+
+#include "rcutiny_plugin.h"
 
 #ifdef CONFIG_NO_HZ
 
@@ -108,8 +106,9 @@ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
  */
 void rcu_sched_qs(int cpu)
 {
-       if (rcu_qsctr_help(&rcu_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk))
-               raise_softirq(RCU_SOFTIRQ);
+       if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
+           rcu_qsctr_help(&rcu_bh_ctrlblk))
+               invoke_rcu_kthread();
 }
 
 /*
@@ -118,7 +117,7 @@ void rcu_sched_qs(int cpu)
 void rcu_bh_qs(int cpu)
 {
        if (rcu_qsctr_help(&rcu_bh_ctrlblk))
-               raise_softirq(RCU_SOFTIRQ);
+               invoke_rcu_kthread();
 }
 
 /*
@@ -134,16 +133,18 @@ void rcu_check_callbacks(int cpu, int user)
                rcu_sched_qs(cpu);
        else if (!in_softirq())
                rcu_bh_qs(cpu);
+       rcu_preempt_check_callbacks();
 }
 
 /*
- * Helper function for rcu_process_callbacks() that operates on the
- * specified rcu_ctrlkblk structure.
+ * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
+ * whose grace period has elapsed.
  */
-static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
+static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
 {
        struct rcu_head *next, *list;
        unsigned long flags;
+       RCU_TRACE(int cb_count = 0);
 
        /* If no RCU callbacks ready to invoke, just return. */
        if (&rcp->rcucblist == rcp->donetail)
@@ -156,6 +157,7 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
        *rcp->donetail = NULL;
        if (rcp->curtail == rcp->donetail)
                rcp->curtail = &rcp->rcucblist;
+       rcu_preempt_remove_callbacks(rcp);
        rcp->donetail = &rcp->rcucblist;
        local_irq_restore(flags);
 
@@ -163,18 +165,60 @@ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
        while (list) {
                next = list->next;
                prefetch(next);
+               debug_rcu_head_unqueue(list);
+               local_bh_disable();
                list->func(list);
+               local_bh_enable();
                list = next;
+               RCU_TRACE(cb_count++);
        }
+       RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
 }
 
 /*
- * Invoke any callbacks whose grace period has completed.
+ * This kthread invokes RCU callbacks whose grace periods have
+ * elapsed.  It is awakened as needed, and takes the place of the
+ * RCU_SOFTIRQ that was used previously for this purpose.
+ * This is a kthread, but it is never stopped, at least not until
+ * the system goes down.
  */
-static void rcu_process_callbacks(struct softirq_action *unused)
+static int rcu_kthread(void *arg)
 {
-       __rcu_process_callbacks(&rcu_ctrlblk);
-       __rcu_process_callbacks(&rcu_bh_ctrlblk);
+       unsigned long work;
+       unsigned long morework;
+       unsigned long flags;
+
+       for (;;) {
+               wait_event_interruptible(rcu_kthread_wq,
+                                        have_rcu_kthread_work != 0);
+               morework = rcu_boost();
+               local_irq_save(flags);
+               work = have_rcu_kthread_work;
+               have_rcu_kthread_work = morework;
+               local_irq_restore(flags);
+               if (work) {
+                       rcu_process_callbacks(&rcu_sched_ctrlblk);
+                       rcu_process_callbacks(&rcu_bh_ctrlblk);
+                       rcu_preempt_process_callbacks();
+               }
+               schedule_timeout_interruptible(1); /* Leave CPU for others. */
+       }
+
+       return 0;  /* Not reached, but needed to shut gcc up. */
+}
+
+/*
+ * Wake up rcu_kthread() to process callbacks now eligible for invocation
+ * or to boost readers.
+ */
+static void invoke_rcu_kthread(void)
+{
+       unsigned long flags;
+
+       local_irq_save(flags);
+       have_rcu_kthread_work = 1;
+       wake_up(&rcu_kthread_wq);
+       local_irq_restore(flags);
 }
 
 /*
@@ -187,7 +231,8 @@ static void rcu_process_callbacks(struct softirq_action *unused)
  *
  * Cool, huh?  (Due to Josh Triplett.)
  *
- * But we want to make this a static inline later.
+ * But we want to make this a static inline later.  The cond_resched()
+ * currently makes this problematic.
  */
 void synchronize_sched(void)
 {
@@ -195,12 +240,6 @@ void synchronize_sched(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_sched);
 
-void synchronize_rcu_bh(void)
-{
-       synchronize_sched();
-}
-EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
-
 /*
  * Helper function for call_rcu() and call_rcu_bh().
  */
@@ -210,25 +249,27 @@ static void __call_rcu(struct rcu_head *head,
 {
        unsigned long flags;
 
+       debug_rcu_head_queue(head);
        head->func = func;
        head->next = NULL;
 
        local_irq_save(flags);
        *rcp->curtail = head;
        rcp->curtail = &head->next;
+       RCU_TRACE(rcp->qlen++);
        local_irq_restore(flags);
 }
 
 /*
- * Post an RCU callback to be invoked after the end of an RCU grace
+ * Post an RCU callback to be invoked after the end of an RCU-sched grace
  * period.  But since we have but one CPU, that would be after any
  * quiescent state.
  */
-void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
+void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 {
-       __call_rcu(head, func, &rcu_ctrlblk);
+       __call_rcu(head, func, &rcu_sched_ctrlblk);
 }
-EXPORT_SYMBOL_GPL(call_rcu);
+EXPORT_SYMBOL_GPL(call_rcu_sched);
 
 /*
  * Post an RCU bottom-half callback to be invoked after any subsequent
@@ -240,27 +281,17 @@ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
 }
 EXPORT_SYMBOL_GPL(call_rcu_bh);
 
-void rcu_barrier(void)
-{
-       struct rcu_synchronize rcu;
-
-       init_completion(&rcu.completion);
-       /* Will wake me after RCU finished. */
-       call_rcu(&rcu.head, wakeme_after_rcu);
-       /* Wait for it. */
-       wait_for_completion(&rcu.completion);
-}
-EXPORT_SYMBOL_GPL(rcu_barrier);
-
 void rcu_barrier_bh(void)
 {
        struct rcu_synchronize rcu;
 
+       init_rcu_head_on_stack(&rcu.head);
        init_completion(&rcu.completion);
        /* Will wake me after RCU finished. */
        call_rcu_bh(&rcu.head, wakeme_after_rcu);
        /* Wait for it. */
        wait_for_completion(&rcu.completion);
+       destroy_rcu_head_on_stack(&rcu.head);
 }
 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 
@@ -268,15 +299,26 @@ void rcu_barrier_sched(void)
 {
        struct rcu_synchronize rcu;
 
+       init_rcu_head_on_stack(&rcu.head);
        init_completion(&rcu.completion);
        /* Will wake me after RCU finished. */
        call_rcu_sched(&rcu.head, wakeme_after_rcu);
        /* Wait for it. */
        wait_for_completion(&rcu.completion);
+       destroy_rcu_head_on_stack(&rcu.head);
 }
 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 
-void __init rcu_init(void)
+/*
+ * Spawn the kthread that invokes RCU callbacks.
+ */
+static int __init rcu_spawn_kthreads(void)
 {
-       open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+       struct sched_param sp;
+
+       rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
+       sp.sched_priority = RCU_BOOST_PRIO;
+       sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
+       return 0;
 }
+early_initcall(rcu_spawn_kthreads);