linux-kernel - Re: [RFC PATCH V2 0/3] sched/fair: Fix nr-running vs delayed-dequeue

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Message-ID: <CAB8ipk-pmSGoaxtMGhcvn7MmSEibvQDbCDgjp9iEDTzG5=_L7g@mail.gmail.com>
Date: Tue, 4 Mar 2025 09:56:34 +0800
From: Xuewen Yan <xuewen.yan94@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Xuewen Yan <xuewen.yan@...soc.com>, vincent.guittot@...aro.org, mingo@...hat.com, 
	juri.lelli@...hat.com, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, vschneid@...hat.com, 
	linux-kernel@...r.kernel.org, ke.wang@...soc.com, di.shen@...soc.com
Subject: Re: [RFC PATCH V2 0/3] sched/fair: Fix nr-running vs delayed-dequeue

Hi Peter

On Mon, Mar 3, 2025 at 8:00 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Mon, Mar 03, 2025 at 06:52:38PM +0800, Xuewen Yan wrote:
> > Delayed dequeued feature keeps a sleeping sched_entitiy enqueued until its
> > lag has elapsed. As a result, it stays also visible in rq->nr_running.
> > However, sometimes when using nr-running, we should not consider
> > sched-delayed tasks.
> > This serie fixes those by adding a helper function which return the
> > number of sched-delayed tasks. And when we should get the real runnable
> > tasks, we sub the nr-delayed tasks.
> >
>
> Is there an actual performance improvement? Because when a runqueue
> looses competition, delayed tasks very quickly dissipate.

At the moment, I don't have very detailed test data. I've been
studying delay-dequeue carefully recently, and these are the issues I
feel might need modification as I go through the code.

Thanks!

BR