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[PATCH 3/2] sched/fair: Skip __update_load_avg() on cfs_rq sched_entities

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  [PATCH 3/2] sched/fair: Skip __update_load_avg() on cfs_rq  sched_entities Tejun Heo <tj@kernel.org> - 2017-04-24 23:40 +0200
    Re: [PATCH 3/2] sched/fair: Skip __update_load_avg() on cfs_rq  sched_entities Peter Zijlstra <peterz@infradead.org> - 2017-04-24 23:50 +0200
      Re: [PATCH 3/2] sched/fair: Skip __update_load_avg() on cfs_rq  sched_entities Tejun Heo <tj@kernel.org> - 2017-04-25 01:00 +0200
    Re: [PATCH 3/2] sched/fair: Skip __update_load_avg() on cfs_rq  sched_entities Tejun Heo <tj@kernel.org> - 2017-04-25 23:20 +0200

#1630043 — [PATCH 3/2] sched/fair: Skip __update_load_avg() on cfs_rq sched_entities

Now that a cfs_rq sched_entity's load_avg always gets propagated from
the associated cfs_rq, there's no point in calling __update_load_avg()
on it.  The two mechanisms compete with each other and we'd be always
using a value close to the propagated one anyway.

Skip __update_load_avg() for cfs_rq sched_entities.  Also, relocate
propagate_entity_load_avg() to signify that propagation is the
counterpart to __update_load_avg() for cfs_rq sched_entities.  This
puts the propagation before update_cfs_rq_load_avg() which shouldn't
disturb anything.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Turner <pjt@google.com>
---
Hello,

A follow-up patch.  This removes __update_load_avg() on cfs_rq se's as
the value is now constantly kept in sync from cfs_rq.  The patch
doesn't cause any noticable changes in tets.

Thanks.

 kernel/sched/fair.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3293,20 +3293,22 @@ static inline void update_load_avg(struc
 	u64 now = cfs_rq_clock_task(cfs_rq);
 	struct rq *rq = rq_of(cfs_rq);
 	int cpu = cpu_of(rq);
-	int decayed;
+	int decayed = 0;
 
 	/*
 	 * Track task load average for carrying it to new CPU after migrated, and
 	 * track group sched_entity load average for task_h_load calc in migration
 	 */
-	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD)) {
-		__update_load_avg(now, cpu, &se->avg,
-			  se->on_rq * scale_load_down(se->load.weight),
-			  cfs_rq->curr == se, NULL);
+	if (entity_is_task(se)) {
+		if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
+			__update_load_avg(now, cpu, &se->avg,
+					  se->on_rq * scale_load_down(se->load.weight),
+					  cfs_rq->curr == se, NULL);
+	} else {
+		decayed |= propagate_entity_load_avg(se);
 	}
 
-	decayed  = update_cfs_rq_load_avg(now, cfs_rq, true);
-	decayed |= propagate_entity_load_avg(se);
+	decayed |= update_cfs_rq_load_avg(now, cfs_rq, true);
 
 	if (decayed && (flags & UPDATE_TG))
 		update_tg_load_avg(cfs_rq, 0);

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#1630060

On Mon, Apr 24, 2017 at 02:35:28PM -0700, Tejun Heo wrote:
> -	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD)) {
> -		__update_load_avg(now, cpu, &se->avg,
> -			  se->on_rq * scale_load_down(se->load.weight),
> -			  cfs_rq->curr == se, NULL);
> +	if (entity_is_task(se)) {
> +		if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
> +			__update_load_avg(now, cpu, &se->avg,
> +					  se->on_rq * scale_load_down(se->load.weight),
> +					  cfs_rq->curr == se, NULL);

I've not looked at these patches yet, but you've been patching old code.
__update_load_avg() no longer exists (the conversion shouldn't be too
hard, its mostly been a restructure/rename thing).

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#1630100

Hello, Peter.

On Mon, Apr 24, 2017 at 11:48:59PM +0200, Peter Zijlstra wrote:
> On Mon, Apr 24, 2017 at 02:35:28PM -0700, Tejun Heo wrote:
> > -	if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD)) {
> > -		__update_load_avg(now, cpu, &se->avg,
> > -			  se->on_rq * scale_load_down(se->load.weight),
> > -			  cfs_rq->curr == se, NULL);
> > +	if (entity_is_task(se)) {
> > +		if (se->avg.last_update_time && !(flags & SKIP_AGE_LOAD))
> > +			__update_load_avg(now, cpu, &se->avg,
> > +					  se->on_rq * scale_load_down(se->load.weight),
> > +					  cfs_rq->curr == se, NULL);
> 
> I've not looked at these patches yet, but you've been patching old code.
> __update_load_avg() no longer exists (the conversion shouldn't be too
> hard, its mostly been a restructure/rename thing).

Ah, sure.  The patchset still being RFC, I wanted to post the version
I was working with.  If you want the patchset refreshed now, please
let me know.

Thanks.

-- 
tejun

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#1631001

On Mon, Apr 24, 2017 at 02:35:28PM -0700, Tejun Heo wrote:
> Now that a cfs_rq sched_entity's load_avg always gets propagated from
> the associated cfs_rq, there's no point in calling __update_load_avg()
> on it.  The two mechanisms compete with each other and we'd be always
> using a value close to the propagated one anyway.
> 
> Skip __update_load_avg() for cfs_rq sched_entities.  Also, relocate
> propagate_entity_load_avg() to signify that propagation is the
> counterpart to __update_load_avg() for cfs_rq sched_entities.  This
> puts the propagation before update_cfs_rq_load_avg() which shouldn't
> disturb anything.

Please ignore this patch.  As we don't propagate on decays, we still
need __update_load_avg() on runanble_load_avg so that it can decay on
its own.

Thanks.

-- 
tejun

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