From: Mel Gorman <mgorman@techsingularity.net>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Barry Song <song.bao.hua@hisilicon.com>,
Juri Lelli <juri.lelli@redhat.com>,
Peter Ziljstra <peterz@infradead.org>,
Aubrey Li <aubrey.li@linux.intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@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 11:30:30 +0000 [thread overview]
Message-ID: <20201204113030.GZ3371@techsingularity.net> (raw)
In-Reply-To: <CAKfTPtBGsXb0RqE_qs2miZGi_uax4VY1_8y1NGhQ17Q8mBx8dw@mail.gmail.com>
On Fri, Dec 04, 2020 at 11:56:36AM +0100, Vincent Guittot wrote:
> > The intent was that the sibling might still be an idle candidate. In
> > the current draft of the series, I do not even clear this so that the
> > SMT sibling is considered as an idle candidate. The reasoning is that if
> > there are no idle cores then an SMT sibling of the target is as good an
> > idle CPU to select as any.
>
> Isn't the purpose of select_idle_smt ?
>
Only in part.
> select_idle_core() looks for an idle core and opportunistically saves
> an idle CPU candidate to skip select_idle_cpu. In this case this is
> useless loops for select_idle_core() because we are sure that the core
> is not idle
>
If select_idle_core() finds an idle candidate other than the sibling,
it'll use it if there is no idle core -- it picks a busy sibling based
on a linear walk of the cpumask. Similarly, select_idle_cpu() is not
guaranteed to scan the sibling first (ordering) or even reach the sibling
(throttling). select_idle_smt() is a last-ditch effort.
--
Mel Gorman
SUSE Labs
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next prev parent reply other threads:[~2020-12-04 11:31 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 [this message]
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
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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