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Subject[PATCH] reduce calls to hrtimer_get_softirq_time
It seems that hrtimer_run_queues() is calling hrtimer_get_softirq_time()
more often than it needs to. This can cause frequent contention on
systems with large numbers of processors/cores.

With this patch, hrtimer_run_queues only calls hrtimer_get_softirq_time()
if there is a pending timer in one of the hrtimer bases, and only once.

This also combines hrtimer_run_queues() and the inline run_hrtimer_queue()
into one function.

Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>

Index: linux/kernel/hrtimer.c
===================================================================
--- linux.orig/kernel/hrtimer.c 2008-04-14 14:03:08.000000000 -0500
+++ linux/kernel/hrtimer.c 2008-04-14 15:35:19.594941220 -0500
@@ -1238,51 +1238,52 @@ void hrtimer_run_pending(void)
/*
* Called from hardirq context every jiffy
*/
-static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base,
- int index)
+void hrtimer_run_queues(void)
{
struct rb_node *node;
- struct hrtimer_clock_base *base = &cpu_base->clock_base[index];
+ struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
+ struct hrtimer_clock_base *base;
+ int index;
+ int gst = 1;

- if (!base->first)
+ if (hrtimer_hres_active())
return;

- if (base->get_softirq_time)
- base->softirq_time = base->get_softirq_time();
+ for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
+ base = &cpu_base->clock_base[index];

- spin_lock(&cpu_base->lock);
-
- while ((node = base->first)) {
- struct hrtimer *timer;
-
- timer = rb_entry(node, struct hrtimer, node);
- if (base->softirq_time.tv64 <= timer->expires.tv64)
- break;
-
- if (timer->cb_mode == HRTIMER_CB_SOFTIRQ) {
- __remove_hrtimer(timer, base, HRTIMER_STATE_PENDING, 0);
- list_add_tail(&timer->cb_entry,
- &base->cpu_base->cb_pending);
+ if (!base->first)
continue;
+
+ if (gst) {
+ hrtimer_get_softirq_time(cpu_base);
+ gst = 0;
}

- __run_hrtimer(timer);
- }
- spin_unlock(&cpu_base->lock);
-}
+ if (base->get_softirq_time)
+ base->softirq_time = base->get_softirq_time();

-void hrtimer_run_queues(void)
-{
- struct hrtimer_cpu_base *cpu_base = &__get_cpu_var(hrtimer_bases);
- int i;
+ spin_lock(&cpu_base->lock);

- if (hrtimer_hres_active())
- return;
+ while ((node = base->first)) {
+ struct hrtimer *timer;

- hrtimer_get_softirq_time(cpu_base);
+ timer = rb_entry(node, struct hrtimer, node);
+ if (base->softirq_time.tv64 <= timer->expires.tv64)
+ break;
+
+ if (timer->cb_mode == HRTIMER_CB_SOFTIRQ) {
+ __remove_hrtimer(timer, base,
+ HRTIMER_STATE_PENDING, 0);
+ list_add_tail(&timer->cb_entry,
+ &base->cpu_base->cb_pending);
+ continue;
+ }

- for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
- run_hrtimer_queue(cpu_base, i);
+ __run_hrtimer(timer);
+ }
+ spin_unlock(&cpu_base->lock);
+ }
}

/*

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