From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
Aubrey Li <aubrey.li@linux.intel.com>,
Barry Song <song.bao.hua@hisilicon.com>,
Ingo Molnar <mingo@redhat.com>,
Peter Ziljstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Linux-ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU
Date: Tue, 8 Dec 2020 14:24:32 +0100 [thread overview]
Message-ID: <CAKfTPtBgo5vCrN87fqKjyaowONLMWeUusLmvE4bmGmDq10+Yrw@mail.gmail.com> (raw)
In-Reply-To: <20201208105900.GG3371@techsingularity.net>
On Tue, 8 Dec 2020 at 11:59, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Tue, Dec 08, 2020 at 11:07:19AM +0100, Dietmar Eggemann wrote:
> > On 07/12/2020 10:15, Mel Gorman wrote:
> > > SIS_AVG_CPU was introduced as a means of avoiding a search when the
> > > average search cost indicated that the search would likely fail. It
> > > was a blunt instrument and disabled by 4c77b18cf8b7 ("sched/fair: Make
> > > select_idle_cpu() more aggressive") and later replaced with a proportional
> > > search depth by 1ad3aaf3fcd2 ("sched/core: Implement new approach to
> > > scale select_idle_cpu()").
> > >
> > > While there are corner cases where SIS_AVG_CPU is better, it has now been
> > > disabled for almost three years. As the intent of SIS_PROP is to reduce
> > > the time complexity of select_idle_cpu(), lets drop SIS_AVG_CPU and focus
> > > on SIS_PROP as a throttling mechanism.
> > >
> > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> > > ---
> > > kernel/sched/fair.c | 3 ---
> > > kernel/sched/features.h | 1 -
> > > 2 files changed, 4 deletions(-)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index 98075f9ea9a8..23934dbac635 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -6161,9 +6161,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> > > avg_idle = this_rq()->avg_idle / 512;
> > > avg_cost = this_sd->avg_scan_cost + 1;
> > >
> > > - if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost)
> > > - return -1;
> > > -
> > > if (sched_feat(SIS_PROP)) {
> > > u64 span_avg = sd->span_weight * avg_idle;
> > > if (span_avg > 4*avg_cost)
> >
> > Nitpick:
> >
> > Since now avg_cost and avg_idle are only used w/ SIS_PROP, they could go
> > completely into the SIS_PROP if condition.
> >
>
> Yeah, I can do that. In the initial prototype, that happened in a
> separate patch that split out SIS_PROP into a helper function and I
> never merged it back. It's a trivial change.
while doing this, should you also put the update of
this_sd->avg_scan_cost under the SIS_PROP feature ?
>
> Thanks.
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2020-12-08 13:25 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 9:15 [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-07 9:15 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-07 15:05 ` Vincent Guittot
2020-12-08 10:07 ` Dietmar Eggemann
2020-12-08 10:59 ` Mel Gorman
2020-12-08 13:24 ` Vincent Guittot [this message]
2020-12-08 13:36 ` Mel Gorman
2020-12-08 13:43 ` Vincent Guittot
2020-12-08 13:53 ` Mel Gorman
2020-12-08 14:47 ` Vincent Guittot
2020-12-08 15:12 ` Mel Gorman
2020-12-08 15:19 ` Vincent Guittot
2020-12-07 9:15 ` [PATCH 2/4] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-08 9:57 ` Dietmar Eggemann
2020-12-08 11:02 ` Mel Gorman
2020-12-07 9:15 ` [PATCH 3/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-07 15:06 ` Vincent Guittot
2020-12-07 9:15 ` [PATCH 4/4] sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling Mel Gorman
2020-12-07 15:04 ` [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Vincent Guittot
2020-12-07 15:42 ` Mel Gorman
2020-12-08 2:06 ` Li, Aubrey
2020-12-08 15:34 [PATCH 0/4] Reduce " Mel Gorman
2020-12-08 15:34 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-08 16:13 ` Vincent Guittot
2021-01-25 8:59 [PATCH v4 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-25 8:59 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2021-01-27 13:51 [PATCH v5 0/4] Scan for an idle sibling in a single pass Mel Gorman
2021-01-27 13:52 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
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