| Date | Wed, 16 Dec 2009 19:55:09 -0800 | From | Greg KH <> | Subject | [012/151] sched: Check for an idle shared cache in select_task_rq_fair() |
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2.6.32-stable review patch. If anyone has any objections, please let us know.
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From: Mike Galbraith <efault@gmx.de>
commit a1f84a3ab8e002159498814eaa7e48c33752b04b upstream.
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> LKML-Reference: <1256654138.17752.7.camel@marge.simson.net> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/sched_fair.c | 33 +++++++++++++++++++++++++++++---- 1 file changed, 29 insertions(+), 4 deletions(-)
--- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1398,11 +1398,36 @@ static int select_task_rq_fair(struct ta 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; - affine_sd = tmp; - want_affine = 0; + 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)
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