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authorjohn stultz <johnstul@us.ibm.com>2007-07-21 04:37:35 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-21 17:49:15 -0700
commit3704540b48295253bd9c87a5e7ff545f9d47a3b8 (patch)
tree081647bba6b901bfaa7e7216ed2f23c42ecee75d /kernel
parent5590a536c0bc403fc73908c66c1c88cbed735ecb (diff)
downloadblackbird-op-linux-3704540b48295253bd9c87a5e7ff545f9d47a3b8.tar.gz
blackbird-op-linux-3704540b48295253bd9c87a5e7ff545f9d47a3b8.zip
tick management: spread timer interrupt
After discussing w/ Thomas over IRC, it seems the issue is the sched tick fires on every cpu at the same time, causing extra lock contention. This smaller change, adds an extra offset per cpu so the ticks don't line up. This patch also drops the idle latency from 40us down to under 20us. Signed-off-by: john stultz <johnstul@us.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/tick-sched.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 52db9e3c526e..b416995b9757 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -546,6 +546,7 @@ void tick_setup_sched_timer(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
ktime_t now = ktime_get();
+ u64 offset;
/*
* Emulate tick processing via per-CPU hrtimers:
@@ -554,8 +555,12 @@ void tick_setup_sched_timer(void)
ts->sched_timer.function = tick_sched_timer;
ts->sched_timer.cb_mode = HRTIMER_CB_IRQSAFE_NO_SOFTIRQ;
- /* Get the next period */
+ /* Get the next period (per cpu) */
ts->sched_timer.expires = tick_init_jiffy_update();
+ offset = ktime_to_ns(tick_period) >> 1;
+ do_div(offset, NR_CPUS);
+ offset *= smp_processor_id();
+ ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);
for (;;) {
hrtimer_forward(&ts->sched_timer, now, tick_period);
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