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Date: Wed, 19 Jul 2023 21:29:14 +0800
From: Aaron Lu <aaron.lu@...el.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
CC: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Daniel Jordan <daniel.m.jordan@...cle.com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>,
"Mel Gorman" <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Valentin Schneider <vschneid@...hat.com>,
Tim Chen <tim.c.chen@...el.com>,
Nitin Tekchandani <nitin.tekchandani@...el.com>,
Yu Chen <yu.c.chen@...el.com>,
Waiman Long <longman@...hat.com>,
<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 3/4] sched/fair: delay update_tg_load_avg() for
cfs_rq's removed load
On Wed, Jul 19, 2023 at 11:47:06AM +0200, Vincent Guittot wrote:
> On Wed, 19 Jul 2023 at 10:01, Aaron Lu <aaron.lu@...el.com> wrote:
> >
> > On Wed, Jul 19, 2023 at 01:18:26PM +0800, Aaron Lu wrote:
> > > Alternatively, I can remove some callsites of update_tg_load_avg() like
> > > you suggested below and only call update_tg_load_avg() when cfs_rq is
> > > decayed(really just decayed, not when it detected it has removed load
> > > pending or load propagated from its children). This way it would give us
> > > similar result as above(roughly once per ms).
> >
> > Something like this: (I think this is better since it removed those
> > unnecessary calls to update_tg_load_avg(), although it is inline but
> > still)
> >
> >
> > From bc749aaefa6bed36aa946921a4006b3dddb69b77 Mon Sep 17 00:00:00 2001
> > From: Aaron Lu <aaron.lu@...el.com>
> > Date: Wed, 19 Jul 2023 13:54:48 +0800
> > Subject: [PATCH] sched/fair: only update_tg_load_avg() when cfs_rq decayed
> >
> > ---
> > kernel/sched/fair.c | 22 +++++++---------------
> > 1 file changed, 7 insertions(+), 15 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a80a73909dc2..7d5b7352b8b5 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3913,16 +3913,16 @@ static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum
> > }
> >
> > /* Update task and its cfs_rq load average */
> > -static inline int propagate_entity_load_avg(struct sched_entity *se)
> > +static inline void propagate_entity_load_avg(struct sched_entity *se)
> > {
> > struct cfs_rq *cfs_rq, *gcfs_rq;
> >
> > if (entity_is_task(se))
> > - return 0;
> > + return;
> >
> > gcfs_rq = group_cfs_rq(se);
> > if (!gcfs_rq->propagate)
> > - return 0;
> > + return;
> >
> > gcfs_rq->propagate = 0;
> >
> > @@ -3936,8 +3936,6 @@ static inline int propagate_entity_load_avg(struct sched_entity *se)
> >
> > trace_pelt_cfs_tp(cfs_rq);
> > trace_pelt_se_tp(se);
> > -
> > - return 1;
> > }
> >
> > /*
> > @@ -3974,9 +3972,8 @@ static inline bool skip_blocked_update(struct sched_entity *se)
> >
> > static inline void update_tg_load_avg(struct cfs_rq *cfs_rq) {}
> >
> > -static inline int propagate_entity_load_avg(struct sched_entity *se)
> > +static inline void propagate_entity_load_avg(struct sched_entity *se)
> > {
> > - return 0;
> > }
> >
> > static inline void add_tg_cfs_propagate(struct cfs_rq *cfs_rq, long runnable_sum) {}
> > @@ -4086,7 +4083,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> > {
> > unsigned long removed_load = 0, removed_util = 0, removed_runnable = 0;
> > struct sched_avg *sa = &cfs_rq->avg;
> > - int decayed = 0;
> > + int decayed;
> >
> > if (cfs_rq->removed.nr) {
> > unsigned long r;
> > @@ -4134,11 +4131,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
> > */
> > add_tg_cfs_propagate(cfs_rq,
> > -(long)(removed_runnable * divider) >> SCHED_CAPACITY_SHIFT);
> > -
> > - decayed = 1;
> > }
> >
> > - decayed |= __update_load_avg_cfs_rq(now, cfs_rq);
> > + decayed = __update_load_avg_cfs_rq(now, cfs_rq);
> > u64_u32_store_copy(sa->last_update_time,
> > cfs_rq->last_update_time_copy,
> > sa->last_update_time);
> > @@ -4252,7 +4247,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> > __update_load_avg_se(now, cfs_rq, se);
> >
> > decayed = update_cfs_rq_load_avg(now, cfs_rq);
> > - decayed |= propagate_entity_load_avg(se);
> > + propagate_entity_load_avg(se);
>
> but then you also skip the call to cfs_rq_util_change()
Ah right, I missed that, thanks for catching this.
Updated:
>From 09a649f8111cfca656b7b735da975ef607b00956 Mon Sep 17 00:00:00 2001
From: Aaron Lu <aaron.lu@...el.com>
Date: Wed, 19 Jul 2023 13:54:48 +0800
Subject: [PATCH] sched/fair: only update_tg_load_avg() when cfs_rq decayed
---
kernel/sched/fair.c | 17 ++++++-----------
1 file changed, 6 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a80a73909dc2..8d4b9e0a19b6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4086,7 +4086,7 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
{
unsigned long removed_load = 0, removed_util = 0, removed_runnable = 0;
struct sched_avg *sa = &cfs_rq->avg;
- int decayed = 0;
+ int decayed;
if (cfs_rq->removed.nr) {
unsigned long r;
@@ -4134,11 +4134,9 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
*/
add_tg_cfs_propagate(cfs_rq,
-(long)(removed_runnable * divider) >> SCHED_CAPACITY_SHIFT);
-
- decayed = 1;
}
- decayed |= __update_load_avg_cfs_rq(now, cfs_rq);
+ decayed = __update_load_avg_cfs_rq(now, cfs_rq);
u64_u32_store_copy(sa->last_update_time,
cfs_rq->last_update_time_copy,
sa->last_update_time);
@@ -4242,7 +4240,7 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
{
u64 now = cfs_rq_clock_pelt(cfs_rq);
- int decayed;
+ int decayed, propagated;
/*
* Track task load average for carrying it to new CPU after migrated, and
@@ -4252,7 +4250,7 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
__update_load_avg_se(now, cfs_rq, se);
decayed = update_cfs_rq_load_avg(now, cfs_rq);
- decayed |= propagate_entity_load_avg(se);
+ propagated = propagate_entity_load_avg(se);
if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
@@ -4264,19 +4262,16 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
* IOW we're enqueueing a task on a new CPU.
*/
attach_entity_load_avg(cfs_rq, se);
- update_tg_load_avg(cfs_rq);
-
} else if (flags & DO_DETACH) {
/*
* DO_DETACH means we're here from dequeue_entity()
* and we are migrating task out of the CPU.
*/
detach_entity_load_avg(cfs_rq, se);
- update_tg_load_avg(cfs_rq);
- } else if (decayed) {
+ } else if (decayed || propagated) {
cfs_rq_util_change(cfs_rq, 0);
- if (flags & UPDATE_TG)
+ if (decayed && (flags & UPDATE_TG))
update_tg_load_avg(cfs_rq);
}
}
--
2.41.0
> >
> > if (!se->avg.last_update_time && (flags & DO_ATTACH)) {
> >
> > @@ -4264,15 +4259,12 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> > * IOW we're enqueueing a task on a new CPU.
> > */
> > attach_entity_load_avg(cfs_rq, se);
> > - update_tg_load_avg(cfs_rq);
> > -
> > } else if (flags & DO_DETACH) {
> > /*
> > * DO_DETACH means we're here from dequeue_entity()
> > * and we are migrating task out of the CPU.
> > */
> > detach_entity_load_avg(cfs_rq, se);
> > - update_tg_load_avg(cfs_rq);
> > } else if (decayed) {
> > cfs_rq_util_change(cfs_rq, 0);
> >
> > --
> > 2.41.0
> >
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