From: Peter Zijlstra <peterz@infradead.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: "Li, Aubrey" <aubrey.li@linux.intel.com>,
Aubrey Li <aubrey.li@intel.com>, Ingo Molnar <mingo@redhat.com>,
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@techsingularity.net>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Andi Kleen <ak@linux.intel.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>
Subject: Re: [PATCH v2] sched/fair: reduce long-tail newly idle balance cost
Date: Tue, 23 Mar 2021 15:49:45 +0100 [thread overview]
Message-ID: <YFoACa0+cGBDxWSF@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAKfTPtCauiWo1yf90XnHK0HKZhS=dPVuJQ6C5gFSLF5_QA-OwA@mail.gmail.com>
On Tue, Mar 23, 2021 at 02:44:57PM +0100, Vincent Guittot wrote:
> Hi Aurey,
>
> On Tue, 16 Mar 2021 at 05:27, Li, Aubrey <aubrey.li@linux.intel.com> wrote:
> >
> > On 2021/2/24 16:15, Aubrey Li wrote:
> > > A long-tail load balance cost is observed on the newly idle path,
> > > this is caused by a race window between the first nr_running check
> > > of the busiest runqueue and its nr_running recheck in detach_tasks.
> > >
> > > Before the busiest runqueue is locked, the tasks on the busiest
> > > runqueue could be pulled by other CPUs and nr_running of the busiest
> > > runqueu becomes 1 or even 0 if the running task becomes idle, this
> > > causes detach_tasks breaks with LBF_ALL_PINNED flag set, and triggers
> > > load_balance redo at the same sched_domain level.
> > >
> > > In order to find the new busiest sched_group and CPU, load balance will
> > > recompute and update the various load statistics, which eventually leads
> > > to the long-tail load balance cost.
> > >
> > > This patch clears LBF_ALL_PINNED flag for this race condition, and hence
> > > reduces the long-tail cost of newly idle balance.
> >
> > Ping...
>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Thanks!
next prev parent reply other threads:[~2021-03-23 14:51 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-24 8:15 [PATCH v2] sched/fair: reduce long-tail newly idle balance cost Aubrey Li
2021-03-16 4:27 ` Li, Aubrey
2021-03-23 13:44 ` Vincent Guittot
2021-03-23 14:49 ` Peter Zijlstra [this message]
2021-03-23 15:08 ` [tip: sched/core] sched/fair: Reduce " tip-bot2 for Aubrey Li
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