From: Joel Fernandes <joel@joelfernandes.org>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Vincent Guittot <vincent.guittot@linaro.org>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Patrick Bellasi <patrick.bellasi@arm.com>,
Quentin Perret <quentin.perret@arm.com>,
kernel-team@android.com, Joel Fernandes <joelaf@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/fair: Remove setting task's se->runnable_weight during PELT update
Date: Thu, 12 Jul 2018 01:17:22 -0700 [thread overview]
Message-ID: <20180712081722.GB154647@joelaf.mtv.corp.google.com> (raw)
In-Reply-To: <0aba9bb6-eec7-130e-373f-5f87f192f2d4@arm.com>
On Wed, Jul 11, 2018 at 10:43:28AM +0200, Dietmar Eggemann wrote:
> On 07/11/2018 01:09 AM, Joel Fernandes wrote:
> > On Mon, Jul 09, 2018 at 05:47:53PM +0100, Dietmar Eggemann wrote:
> > > A CFS (SCHED_OTHER, SCHED_BATCH or SCHED_IDLE policy) task's
> > > se->runnable_weight must always be in sync with its se->load.weight.
> > >
> > > se->runnable_weight is set to se->load.weight when the task is
> > > forked (init_entity_runnable_average()) or reniced (reweight_entity()).
> > >
> > > There are two cases in set_load_weight() which since they currently only
> > > set se->load.weight could lead to a situation in which se->load.weight
> > > is different to se->runnable_weight for a CFS task:
> > >
> > > (1) A task switches to SCHED_IDLE.
> > >
> > > (2) A SCHED_FIFO, SCHED_RR or SCHED_DEADLINE task which has been reniced
> > > (during which only its static priority gets set) switches to
> > > SCHED_OTHER or SCHED_BATCH.
> > >
> > > Set se->runnable_weight to se->load.weight in these two cases to prevent
> > > this. This eliminates the need to explicitly set it to se->load.weight
> > > during PELT updates in the CFS scheduler fastpath.
> >
> > Looks good to me. By the way just asking, is there a chance where
> > se_weight(se) and se_runnable(se) can ever be different?
>
> Yes they can be different, not for a task though but for se's representing
> task groups. It got introduced to be able to propagate load and runnable
> load independently through the task groups hierarchies.
I know that task-group se has different values. I was saying for task ses,
the extra division can be skipped possibly improving performance (if at all).
thanks,
- Joel
next prev parent reply other threads:[~2018-07-12 8:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-09 16:47 Dietmar Eggemann
2018-07-10 23:09 ` Joel Fernandes
2018-07-11 8:43 ` Dietmar Eggemann
2018-07-12 8:17 ` Joel Fernandes [this message]
2018-07-13 14:57 ` Dietmar Eggemann
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