From: Tejun Heo <tj@kernel.org>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Christopher Lameter <cl@linux.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
David Rientjes <rientjes@google.com>,
Pekka Enberg <penberg@kernel.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
John Stultz <john.stultz@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Stephen Boyd <sboyd@kernel.org>
Subject: Re: [RFC] mm, slab: reschedule cache_reap() on the same CPU
Date: Tue, 10 Apr 2018 12:53:05 -0700 [thread overview]
Message-ID: <20180410195247.GQ3126663@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <983c61d1-1444-db1f-65c1-3b519ac4d57b@suse.cz>
Hello,
On Tue, Apr 10, 2018 at 09:40:19PM +0200, Vlastimil Babka wrote:
> On 04/10/2018 04:12 PM, Christopher Lameter wrote:
> > On Tue, 10 Apr 2018, Vlastimil Babka wrote:
> >
> >> cache_reap() is initially scheduled in start_cpu_timer() via
> >> schedule_delayed_work_on(). But then the next iterations are scheduled via
> >> schedule_delayed_work(), thus using WORK_CPU_UNBOUND.
> >
> > That is a bug.. cache_reap must run on the same cpu since it deals with
> > the per cpu queues of the current cpu. Scheduled_delayed_work() used to
> > guarantee running on teh same cpu.
>
> Did it? When did it stop? (which stable kernels should we backport to?)
It goes back to v4.5 - ef557180447f ("workqueue: schedule
WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs") which made
WQ_CPU_UNBOUND on percpu workqueues honor wq_unbound_cpusmask so that
cpu isolation works better. Unless the force_rr option or
unbound_cpumask is set, it still follows local cpu.
> So is my assumption correct that without specifying a CPU, the next work
> might be processed on a different cpu than the current one, *and also*
> be executed with a kthread/u* that can migrate to another cpu *in the
> middle of the work*? Tejun?
For percpu work items, they'll keep executing on the same cpu it
started on unless the cpu goes down while executing.
> > schedule_delayed_work_on(smp_processor_id(), work, round_jiffies_relative(REAPTIMEOUT_AC));
> >
> > instead all of the other changes?
>
> If we can rely on that 100%, sure.
Yeah, you can.
Thanks.
--
tejun
next prev parent reply other threads:[~2018-04-10 19:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-10 8:15 [RFC] mm, slab: reschedule cache_reap() on the same CPU Vlastimil Babka
2018-04-10 14:12 ` Christopher Lameter
2018-04-10 14:17 ` Tejun Heo
2018-04-10 19:40 ` Vlastimil Babka
2018-04-10 19:53 ` Tejun Heo [this message]
2018-04-10 20:13 ` Vlastimil Babka
2018-04-10 20:23 ` Tejun Heo
2018-04-11 7:00 ` [PATCH] " Vlastimil Babka
2018-04-11 10:53 ` Pekka Enberg
2018-04-11 13:41 ` Christopher Lameter
2018-04-12 0:47 ` Minchan Kim
2018-04-13 8:44 ` Vlastimil Babka
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