From: Vincent Guittot <vincent.guittot@linaro.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] sched/fair: improve spreading of utilization
Date: Fri, 13 Mar 2020 12:24:05 +0100 [thread overview]
Message-ID: <CAKfTPtCQZMOz9HzdiWg5g9O+W=hC5E-fiG8YVHWCcODjFRfefQ@mail.gmail.com> (raw)
In-Reply-To: <jhjr1xwjz96.mognet@arm.com>
On Fri, 13 Mar 2020 at 12:00, Valentin Schneider
<valentin.schneider@arm.com> wrote:
>
>
> On Thu, Mar 12 2020, Vincent Guittot wrote:
> > kernel/sched/fair.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 3c8a379c357e..97a0307312d9 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -9025,6 +9025,14 @@ static struct rq *find_busiest_queue(struct lb_env *env,
> > case migrate_util:
> > util = cpu_util(cpu_of(rq));
> >
> > + /*
> > + * Don't try to pull utilization from a CPU with one
> > + * running task. Whatever its utilization, we will fail
> > + * detach the task.
> > + */
> > + if (nr_running <= 1)
> > + continue;
> > +
>
> Doesn't this break misfit? If the busiest group is group_misfit_task, it
> is totally valid for the runqueues to have a single running task -
> that's the CPU-bound task we want to upmigrate.
group_misfit_task has its dedicated migrate_misfit case
>
> If the busiest rq has only a single running task, we'll skip the
> detach_tasks() block and go straight to the active balance bits.
> Misfit balancing totally relies on this, and IMO ASYM_PACKING does
> too. Looking at voluntary_active_balance(), it seems your change also
> goes against the one added by
> 1aaf90a4b88a ("sched: Move CFS tasks to CPUs with higher capacity")
>
> The bandaid here would be gate this 'continue' with checks against the
> busiest_group_type, but that's only a loose link wrt
> voluntary_active_balance().
>
> > if (busiest_util < util) {
> > busiest_util = util;
> > busiest = rq;
next prev parent reply other threads:[~2020-03-13 11:24 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 16:54 [PATCH] sched/fair: improve spreading of utilization Vincent Guittot
2020-03-13 10:26 ` Peter Zijlstra
2020-03-13 11:00 ` Valentin Schneider
2020-03-13 11:24 ` Vincent Guittot [this message]
2020-03-13 11:28 ` Valentin Schneider
2020-03-13 12:42 ` Valentin Schneider
2020-03-13 12:55 ` Vincent Guittot
2020-03-13 14:26 ` Vincent Guittot
2020-03-13 15:47 ` Valentin Schneider
2020-03-13 16:09 ` Vincent Guittot
2020-03-13 16:57 ` Valentin Schneider
2020-03-13 17:12 ` Vincent Guittot
2020-03-13 17:34 ` Valentin Schneider
2020-03-20 12:58 ` [tip: sched/core] sched/fair: Improve " tip-bot2 for Vincent Guittot
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