linux-kernel - Re: [PATCH 2/9] sched/fair: Add new cfs_rq.h_nr

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Message-ID: <20241128102741.GE24400@noisy.programming.kicks-ass.net>
Date: Thu, 28 Nov 2024 11:27:41 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Vincent Guittot <vincent.guittot@...aro.org>
Cc: 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,
	kprateek.nayak@....com, pauld@...hat.com, efault@....de,
	luis.machado@....com
Subject: Re: [PATCH 2/9] sched/fair: Add new cfs_rq.h_nr_enqueued

On Thu, Nov 28, 2024 at 11:24:45AM +0100, Vincent Guittot wrote:
> On Thu, 28 Nov 2024 at 10:56, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Thu, Nov 28, 2024 at 10:27:43AM +0100, Vincent Guittot wrote:
> > > With delayed dequeued feature, a sleeping sched_entity remains enqueued
> > > in the rq until its lag has elapsed. As a result, it stays also visible
> > > in the statistics that are used to balance the system and in particular
> > > the field h_nr_running when the sched_entity is associated to a task.
> > >
> > > Create a new h_nr_enqueued that tracks all enqueued tasks and restore the
> > > behavior of h_nr_running i.e. tracking the number of fair tasks that want
> > > to run.
> >
> > Isn't h_nr_enqueued := h_nr_running - h_nr_delayed ? Does it really make
> > sense to have another variable that is so trivially computable?
> 
> I changed h_nr_running to track only running tasks and not delayed dequeue

Yes, that was hidden so well, I couldn't even find it on the second
reading :/