[tip:sched/core] sched: Add a few SYNC hint knobs to play with

tip-bot for Peter Zijlstra
2009-09-16T10:25:18Z

Commit-ID: e69b0f1b41c0e57bb1e29100b5810a5914efcb45
Gitweb: http://git.kernel.org/tip/e69b0f1b41c0e57bb1e29100b5810a5914efcb45
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Tue, 15 Sep 2009 19:38:52 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Tue, 15 Sep 2009 19:47:23 +0200

sched: Add a few SYNC hint knobs to play with

Currently we use overlap to weaken the SYNC hint, but allow it to
set the hint as well.

echo NO_SYNC_WAKEUP > /debug/sched_features
echo SYNC_MORE > /debug/sched_features

preserves pipe-test behaviour without using the WF_SYNC hint.

Worth playing with on more workloads...

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

---
kernel/sched_fair.c | 14 +++++++++++---
kernel/sched_features.h | 10 ++++++++++
2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6766959..280892e 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1165,9 +1165,17 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
load = source_load(prev_cpu, idx);
this_load = target_load(this_cpu, idx);

- if (sync && (curr->se.avg_overlap > sysctl_sched_migration_cost ||
- p->se.avg_overlap > sysctl_sched_migration_cost))
- sync = 0;
+ if (sync) {
+ if (sched_feat(SYNC_LESS) &&
+ (curr->se.avg_overlap > sysctl_sched_migration_cost ||
+ p->se.avg_overlap > sysctl_sched_migration_cost))
+ sync = 0;
+ } else {
+ if (sched_feat(SYNC_MORE) &&
+ (curr->se.avg_overlap < sysctl_sched_migration_cost &&
+ p->se.avg_overlap < sysctl_sched_migration_cost))
+ sync = 1;
+ }

/*
* If sync wakeup then subtract the (maximum possible)
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index 294e10e..70115c6 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -63,6 +63,16 @@ SCHED_FEAT(SYNC_WAKEUPS, 1)
SCHED_FEAT(AFFINE_WAKEUPS, 1)

/*
+ * Weaken SYNC hint based on overlap
+ */
+SCHED_FEAT(SYNC_LESS, 1)
+
+/*
+ * Add SYNC hint based on overlap
+ */
+SCHED_FEAT(SYNC_MORE, 0)
+
+/*
* Prefer to schedule the task we woke last (assuming it failed
* wakeup-preemption), since its likely going to consume data we
* touched, increases cache locality.