From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: "Li, Aubrey" <aubrey.li@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
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 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched
Date: Fri, 4 Dec 2020 16:23:48 +0100 [thread overview]
Message-ID: <CAKfTPtBXUK7NnhN1Rxeq-o5t-G+csN6Tj0yP=BSV_sdD1uZS0g@mail.gmail.com> (raw)
In-Reply-To: <20201204143115.GB3371@techsingularity.net>
On Fri, 4 Dec 2020 at 15:31, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Fri, Dec 04, 2020 at 02:47:48PM +0100, Vincent Guittot wrote:
> > > IIUC, select_idle_core and select_idle_cpu share the same cpumask(select_idle_mask)?
> > > If the target's sibling is removed from select_idle_mask from select_idle_core(),
> > > select_idle_cpu() will lose the chance to pick it up?
> >
> > This is only relevant for patch 10 which is not to be included IIUC
> > what mel said in cover letter : "Patches 9 and 10 are stupid in the
> > context of this series."
> >
>
> Patch 10 was stupid in the context of the prototype because
> select_idle_core always returned a CPU. A variation ended up being
> reintroduced at the end of the Series Yet To Be Posted so that SMT siblings
> are cleared during select_idle_core() but select_idle_cpu() still has a
> mask with unvisited CPUs to consider if no idle cores are found.
>
> As far as I know, this would still be compatible with Aubrey's idle
> cpu mask as long as it's visited and cleared between select_idle_core
> and select_idle_cpu. It relaxes the contraints on Aubrey to some extent
> because the idle cpu mask would be a hint so if the information is out
> of date, an idle cpu may still be found the normal way.
But even without patch 10, just replacing sched_domain_span(sd) by
sds_idle_cpus(sd->shared) will ensure that sis loops only on cpus that
get a chance to be idle so select_idle_core is likely to return an
idle_candidate
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2020-12-04 15:24 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-03 14:11 [RFC PATCH 00/10] Reduce time complexity of select_idle_sibling Mel Gorman
2020-12-03 14:11 ` [PATCH 01/10] sched/fair: Track efficiency " Mel Gorman
2020-12-03 14:11 ` [PATCH 02/10] sched/fair: Track efficiency of task recent_used_cpu Mel Gorman
2020-12-03 14:11 ` [PATCH 03/10] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-03 14:11 ` [PATCH 04/10] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-03 16:35 ` Vincent Guittot
2020-12-03 17:50 ` Mel Gorman
2020-12-03 14:11 ` [PATCH 05/10] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-03 14:11 ` [PATCH 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched Mel Gorman
2020-12-03 16:38 ` Vincent Guittot
2020-12-03 17:52 ` Mel Gorman
2020-12-04 10:56 ` Vincent Guittot
2020-12-04 11:30 ` Mel Gorman
2020-12-04 13:13 ` Vincent Guittot
2020-12-04 13:17 ` Vincent Guittot
2020-12-04 13:40 ` Li, Aubrey
2020-12-04 13:47 ` Li, Aubrey
2020-12-04 13:47 ` Vincent Guittot
2020-12-04 14:07 ` Li, Aubrey
2020-12-04 14:31 ` Mel Gorman
2020-12-04 15:23 ` Vincent Guittot [this message]
2020-12-04 15:40 ` Mel Gorman
2020-12-04 15:43 ` Vincent Guittot
2020-12-04 18:41 ` Mel Gorman
2020-12-04 14:27 ` Mel Gorman
2020-12-03 14:11 ` [PATCH 07/10] sched/fair: Account for the idle cpu/smt search cost Mel Gorman
2020-12-03 14:11 ` [PATCH 08/10] sched/fair: Reintroduce SIS_AVG_CPU but in the context of SIS_PROP to reduce search depth Mel Gorman
2020-12-03 14:11 ` [PATCH 09/10] sched/fair: Limit the search for an idle core Mel Gorman
2020-12-03 14:19 ` Mel Gorman
2020-12-03 14:20 ` [PATCH 10/10] sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling Mel Gorman
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