From: Vincent Guittot <vincent.guittot@linaro.org>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: 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 06/10] sched/fair: Clear the target CPU from the cpumask of CPUs searched
Date: Fri, 4 Dec 2020 11:56:36 +0100 [thread overview]
Message-ID: <CAKfTPtBGsXb0RqE_qs2miZGi_uax4VY1_8y1NGhQ17Q8mBx8dw@mail.gmail.com> (raw)
In-Reply-To: <20201203175204.GY3371@techsingularity.net>
On Thu, 3 Dec 2020 at 18:52, Mel Gorman <mgorman@techsingularity.net> wrote:
>
> On Thu, Dec 03, 2020 at 05:38:03PM +0100, Vincent Guittot wrote:
> > On Thu, 3 Dec 2020 at 15:11, Mel Gorman <mgorman@techsingularity.net> wrote:
> > >
> > > The target CPU is definitely not idle in both select_idle_core and
> > > select_idle_cpu. For select_idle_core(), the SMT is potentially
> > > checked unnecessarily as the core is definitely not idle if the
> > > target is busy. For select_idle_cpu(), the first CPU checked is
> > > simply a waste.
> >
> > >
> > > Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
> > > ---
> > > kernel/sched/fair.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index 68dd9cd62fbd..1d8f5c4b4936 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -6077,6 +6077,7 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
> > > return -1;
> > >
> > > cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
> > > + __cpumask_clear_cpu(target, cpus);
> >
> > should clear cpu_smt_mask(target) as we are sure that the core will not be idle
> >
>
> 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 ?
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
>
> --
> Mel Gorman
> SUSE Labs
next prev parent reply other threads:[~2020-12-04 10:57 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAKfTPtBGsXb0RqE_qs2miZGi_uax4VY1_8y1NGhQ17Q8mBx8dw@mail.gmail.com \
--to=vincent.guittot@linaro.org \
--cc=aubrey.li@linux.intel.com \
--cc=juri.lelli@redhat.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mgorman@techsingularity.net \
--cc=mingo@redhat.com \
--cc=peterz@infradead.org \
--cc=song.bao.hua@hisilicon.com \
--cc=valentin.schneider@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).