[tip:sched/core] sched: Check for an idle shared cache in select_task_rq_fair()

tip-bot for Mike Galbraith
2009-11-04T19:34:25Z

Commit-ID: a1f84a3ab8e002159498814eaa7e48c33752b04b
Gitweb: http://git.kernel.org/tip/a1f84a3ab8e002159498814eaa7e48c33752b04b
Author: Mike Galbraith <efault@gmx.de>
AuthorDate: Tue, 27 Oct 2009 15:35:38 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 4 Nov 2009 18:46:22 +0100

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

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>
---
kernel/sched_fair.c | 33 +++++++++++++++++++++++++++++----
1 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 4e777b4..da87385 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -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;

- 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)