The following commit has been merged into the sched/core branch of tip:
Commit-ID: 9abb897345ce1d41257567f571a78137c961c405
Gitweb: https://git.kernel.org/tip/9abb897345ce1d41257567f571a78137c961c405
Author: Peter Oskolkov <posk@xxxxxxxxxx>
AuthorDate: Wed, 30 Sep 2020 10:35:32 -07:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 03 Oct 2020 16:30:52 +02:00
sched/fair: Tweak pick_next_entity()
Currently, pick_next_entity(...) has the following structure
(simplified):
[...]
if (last_buddy_ok())
result = last_buddy;
if (next_buddy_ok())
result = next_buddy;
[...]
The intended behavior is to prefer next buddy over last buddy;
the current code somewhat obfuscates this, and also wastes
cycles checking the last buddy when eventually the next buddy is
picked up.
So this patch refactors two 'ifs' above into
[...]
if (next_buddy_ok())
result = next_buddy;
else if (last_buddy_ok())
result = last_buddy;
[...]
Signed-off-by: Peter Oskolkov <posk@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guitttot@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20200930173532.1069092-1-posk@xxxxxxxxxx
---
kernel/sched/fair.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fc3410b..cec6cf9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4465,17 +4465,17 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
se = second;
}
- /*
- * Prefer last buddy, try to return the CPU to a preempted task.
- */
- if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
- se = cfs_rq->last;
-
- /*
- * Someone really wants this to run. If it's not unfair, run it.
- */
- if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
+ if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) {
+ /*
+ * Someone really wants this to run. If it's not unfair, run it.
+ */
se = cfs_rq->next;
+ } else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) {
+ /*
+ * Prefer last buddy, try to return the CPU to a preempted task.
+ */
+ se = cfs_rq->last;
+ }
clear_buddies(cfs_rq, se);
|