* [PATCH] sched/fair: tweak pick_next_entity
@ 2020-09-30 17:35 Peter Oskolkov
2020-10-01 7:17 ` Vincent Guittot
2020-10-05 7:43 ` [tip: sched/core] sched/fair: Tweak pick_next_entity() tip-bot2 for Peter Oskolkov
0 siblings, 2 replies; 4+ messages in thread
From: Peter Oskolkov @ 2020-09-30 17:35 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, Vincent Guittot, Dietmar Eggemann,
linux-kernel
Cc: Peter Oskolkov, Peter Oskolkov
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@google.com>
---
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 fc3410b8b990..cec6cf9b2bb3 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);
--
2.28.0.709.gb0816b6eb0-goog
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] sched/fair: tweak pick_next_entity
2020-09-30 17:35 [PATCH] sched/fair: tweak pick_next_entity Peter Oskolkov
@ 2020-10-01 7:17 ` Vincent Guittot
2020-10-01 7:33 ` Peter Zijlstra
2020-10-05 7:43 ` [tip: sched/core] sched/fair: Tweak pick_next_entity() tip-bot2 for Peter Oskolkov
1 sibling, 1 reply; 4+ messages in thread
From: Vincent Guittot @ 2020-10-01 7:17 UTC (permalink / raw)
To: Peter Oskolkov
Cc: Ingo Molnar, Peter Zijlstra, Dietmar Eggemann, linux-kernel,
Peter Oskolkov
On Wed, 30 Sep 2020 at 19:35, Peter Oskolkov <posk@google.com> wrote:
>
> 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@google.com>
Reviewed-by: Vincent Guittot <vincent.guitttot@linaro.org>
> ---
> 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 fc3410b8b990..cec6cf9b2bb3 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);
>
> --
> 2.28.0.709.gb0816b6eb0-goog
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] sched/fair: tweak pick_next_entity
2020-10-01 7:17 ` Vincent Guittot
@ 2020-10-01 7:33 ` Peter Zijlstra
0 siblings, 0 replies; 4+ messages in thread
From: Peter Zijlstra @ 2020-10-01 7:33 UTC (permalink / raw)
To: Vincent Guittot
Cc: Peter Oskolkov, Ingo Molnar, Dietmar Eggemann, linux-kernel,
Peter Oskolkov
On Thu, Oct 01, 2020 at 09:17:43AM +0200, Vincent Guittot wrote:
> On Wed, 30 Sep 2020 at 19:35, Peter Oskolkov <posk@google.com> wrote:
> >
> > 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@google.com>
>
> Reviewed-by: Vincent Guittot <vincent.guitttot@linaro.org>
Thanks!
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip: sched/core] sched/fair: Tweak pick_next_entity()
2020-09-30 17:35 [PATCH] sched/fair: tweak pick_next_entity Peter Oskolkov
2020-10-01 7:17 ` Vincent Guittot
@ 2020-10-05 7:43 ` tip-bot2 for Peter Oskolkov
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot2 for Peter Oskolkov @ 2020-10-05 7:43 UTC (permalink / raw)
To: linux-tip-commits
Cc: Peter Oskolkov, Peter Zijlstra (Intel), Vincent Guittot, x86, LKML
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@google.com>
AuthorDate: Wed, 30 Sep 2020 10:35:32 -07:00
Committer: Peter Zijlstra <peterz@infradead.org>
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@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guitttot@linaro.org>
Link: https://lkml.kernel.org/r/20200930173532.1069092-1-posk@google.com
---
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);
^ permalink raw reply related [flat|nested] 4+ messages in thread
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2020-09-30 17:35 [PATCH] sched/fair: tweak pick_next_entity Peter Oskolkov
2020-10-01 7:17 ` Vincent Guittot
2020-10-01 7:33 ` Peter Zijlstra
2020-10-05 7:43 ` [tip: sched/core] sched/fair: Tweak pick_next_entity() tip-bot2 for Peter Oskolkov
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