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sched: Check for an idle shared cache in select_task_rq_fair()

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When waking affine, check for an idle shared cache, and if
found, wake to that CPU/sibling instead of the waker's CPU.

This improves pgsql+oltp ramp up by roughly 8%. Possibly more
for other loads, depending on overlap. The trade-off is a
roughly 1% peak downturn if tasks are truly synchronous.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@kernel.org>
LKML-Reference: <1256654138.17752.7.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Mike Galbraith 2009-10-27 15:35:38 +01:00 committed by Ingo Molnar
parent acc3f5d7ca
commit a1f84a3ab8
1 changed files with 29 additions and 4 deletions
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29
kernel/sched_fair.c
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@ -1372,11 +1372,36 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
want_sd = 0;
}
if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
if (want_affine && (tmp->flags & SD_WAKE_AFFINE)) {
int candidate = -1, i;
if (cpumask_test_cpu(prev_cpu, sched_domain_span(tmp)))
candidate = cpu;
/*
* Check for an idle shared cache.
*/
if (tmp->flags & SD_PREFER_SIBLING) {
if (candidate == cpu) {
if (!cpu_rq(prev_cpu)->cfs.nr_running)
candidate = prev_cpu;
}
if (candidate == -1 || candidate == cpu) {
for_each_cpu(i, sched_domain_span(tmp)) {
if (!cpu_rq(i)->cfs.nr_running) {
candidate = i;
break;
}
}
}
}
if (candidate >= 0) {
affine_sd = tmp;
want_affine = 0;
cpu = candidate;
}
}
if (!want_sd && !want_affine)