linux-kernel - Re: [PATCH 19/24] sched/eevdf: Fixup PELT vs DELAYED

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Message-ID: <CAKfTPtAVibNv0Uuez6xk3U6nUG3yV0p6A5ToLfpT6yv-F4qgyQ@mail.gmail.com>
Date: Mon, 19 Aug 2024 14:50:47 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <vschneid@...hat.com>, mingo@...hat.com, juri.lelli@...hat.com, 
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, 
	mgorman@...e.de, linux-kernel@...r.kernel.org, kprateek.nayak@....com, 
	wuyun.abel@...edance.com, youssefesmat@...omium.org, tglx@...utronix.de, 
	efault@....de
Subject: Re: [PATCH 19/24] sched/eevdf: Fixup PELT vs DELAYED_DEQUEUE

On Sun, 18 Aug 2024 at 01:06, Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Aug 14, 2024 at 02:59:00PM +0200, Vincent Guittot wrote:
>
> > > So the whole reason to keep then enqueued is so that they can continue
> > > to compete for vruntime, and vruntime is load based. So it would be very
> > > weird to remove them from load.
> >
> > We only use the weight to update vruntime, not the load. The load is
> > used to balance tasks between cpus and if we keep a "delayed" dequeued
> > task in the load, we will artificially inflate the load_avg on this rq
>
> So far load has been a direct sum of all weight. Additionally, we delay

it has been the sum of all runnable tasks but delayed tasks are not
runnable anymore. The task stays "enqueued" only to help clearing its
lag

> until a task gets picked again, migrating tasks to other CPUs will
> expedite this condition.
>
> Anyway, at the moment I don't have strong evidence either which way, and
> the above argument seem to suggest not changing things for now.
>
> We can always re-evaluate.