[tip:sched/core] sched: Implement a gentler fair-sleepers feature

tip-bot for Ingo Molnar
2009-09-16T10:25:44Z

Commit-ID: 51e0304ce6e55a6e59658558916b4f74da085ff0
Gitweb: http://git.kernel.org/tip/51e0304ce6e55a6e59658558916b4f74da085ff0
Author: Ingo Molnar <mingo@elte.hu>
AuthorDate: Wed, 16 Sep 2009 08:54:45 +0200
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 16 Sep 2009 09:05:20 +0200

sched: Implement a gentler fair-sleepers feature

Add back FAIR_SLEEPERS and GENTLE_FAIR_SLEEPERS.

FAIR_SLEEPERS is the old logic: credit sleepers with their sleep time.

GENTLE_FAIR_SLEEPERS dampens this a bit: 50% of their sleep time gets
credited.

The hope here is to still give the benefits of fair-sleepers logic
(quick wakeups, etc.) while not allow them to have 100% of their
sleep time as if they were running.

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

---
kernel/sched_fair.c | 9 ++++++++-
kernel/sched_features.h | 9 ++++++++-
2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index a37f311..acf16a8 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -711,7 +711,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)

if (!initial) {
/* sleeps upto a single latency don't count. */
- if (sched_feat(NEW_FAIR_SLEEPERS)) {
+ if (sched_feat(FAIR_SLEEPERS)) {
unsigned long thresh = sysctl_sched_latency;

/*
@@ -725,6 +725,13 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
task_of(se)->policy != SCHED_IDLE))
thresh = calc_delta_fair(thresh, se);

+ /*
+ * Halve their sleep time's effect, to allow
+ * for a gentler effect of sleepers:
+ */
+ if (sched_feat(GENTLE_FAIR_SLEEPERS))
+ thresh >>= 1;
+
vruntime -= thresh;
}
}
diff --git a/kernel/sched_features.h b/kernel/sched_features.h
index 70115c6..fd37567 100644
--- a/kernel/sched_features.h
+++ b/kernel/sched_features.h
@@ -3,7 +3,14 @@
* considers the task to be running during that period. This gives it
* a service deficit on wakeup, allowing it to run sooner.
*/
-SCHED_FEAT(NEW_FAIR_SLEEPERS, 0)
+SCHED_FEAT(FAIR_SLEEPERS, 1)
+
+/*
+ * Only give sleepers 50% of their service deficit. This allows
+ * them to run sooner, but does not allow tons of sleepers to
+ * rip the spread apart.
+ */
+SCHED_FEAT(GENTLE_FAIR_SLEEPERS, 1)

/*
* By not normalizing the sleep time, heavy tasks get an effective