From: Valentin Schneider <valentin.schneider@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Qais Yousef <qais.yousef@arm.com>,
Quentin Perret <qperret@google.com>,
Pavan Kondeti <pkondeti@codeaurora.org>,
Rik van Riel <riel@surriel.com>,
Lingutla Chandrasekhar <clingutla@codeaurora.org>
Subject: Re: [PATCH 2/2] sched/fair: Relax task_hot() for misfit tasks
Date: Fri, 07 May 2021 14:46:59 +0100 [thread overview]
Message-ID: <87y2cqirl8.mognet@arm.com> (raw)
In-Reply-To: <CAKfTPtA+w1Euepw+MP0o1EGYhoohpQm3jJP+WFQrmZ6Zet+F3g@mail.gmail.com>
Hi Vincent, apologies for the belated reply
On 30/04/21 08:58, Vincent Guittot wrote:
> On Wed, 21 Apr 2021 at 12:52, Valentin Schneider
> <valentin.schneider@arm.com> wrote:
>> On 20/04/21 16:33, Vincent Guittot wrote:
>> > Is it something that happens often or just a sporadic/transient state
>> > ? I mean does it really worth the extra complexity and do you see
>> > performance improvement ?
>> >
>>
>> "Unfortunately" yes, this is a relatively common scenario when running "1
>> big task per CPU" types of workloads. The expected behaviour for big.LITTLE
>> systems is to upmigrate tasks stuck on the LITTLE CPUs as soon as a big CPU
>> becomes free, usually via newidle balance (which, since they process work
>> faster than the LITTLEs, is bound to happen), and an extra task being
>> enqueued at "the wrong time" can prevent this from happening.
>>
>> This usually means a misfit task can take a few dozen extra ms than it
>
> A few dozens is quite long. With a big core being idle, it should try
> every 8ms on a quad x quad system and I suspect the next try will be
> during the next tick. Would be good to understand why it has to wait
> so much
>
True, IIRC this was mostly due to a compound effect of the different issues
I've described in that thread (and the previous one). Now that
9bcb959d05ee ("sched/fair: Ignore percpu threads for imbalance pulls")
is in, I'll re-run some tests against upstream and see how we fare.
prev parent reply other threads:[~2021-05-07 13:47 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-15 17:58 [PATCH 0/2] sched/fair: (The return of) misfit task load-balance tweaks Valentin Schneider
2021-04-15 17:58 ` [PATCH 1/2] sched/fair: Filter out locally-unsolvable misfit imbalances Valentin Schneider
2021-04-15 18:47 ` Rik van Riel
2021-04-16 13:29 ` Vincent Guittot
2021-04-19 17:13 ` Valentin Schneider
2021-04-22 9:48 ` Dietmar Eggemann
2021-04-22 19:19 ` Valentin Schneider
2021-04-15 17:58 ` [PATCH 2/2] sched/fair: Relax task_hot() for misfit tasks Valentin Schneider
2021-04-15 20:39 ` Rik van Riel
2021-04-16 9:43 ` Valentin Schneider
2021-04-19 12:59 ` Phil Auld
2021-04-19 17:17 ` Valentin Schneider
2021-04-19 20:23 ` Phil Auld
2021-04-16 13:51 ` Vincent Guittot
2021-04-19 17:13 ` Valentin Schneider
2021-04-20 14:33 ` Vincent Guittot
2021-04-21 10:52 ` Valentin Schneider
2021-04-22 17:29 ` Dietmar Eggemann
2021-04-22 19:19 ` Valentin Schneider
2021-04-30 6:58 ` Vincent Guittot
2021-05-07 13:46 ` Valentin Schneider [this message]
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