linux-kernel - Re: [PATCH 4/4] sched/fair: Merge select_idle

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Message-ID: <CAKfTPtB3_t_FBB21drYbcT7aUp10tZ-rtZ91Rh08+H+a-h==RQ@mail.gmail.com>
Date:   Wed, 27 Jan 2021 14:26:41 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Li Aubrey <aubrey.li@...ux.intel.com>,
        Qais Yousef <qais.yousef@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched/fair: Merge select_idle_core/cpu()

On Wed, 27 Jan 2021 at 14:21, Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> On Wed, Jan 27, 2021 at 02:07:50PM +0100, Vincent Guittot wrote:
> > > @@ -6162,18 +6162,16 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> > >
> > >         for_each_cpu_wrap(cpu, cpus, target) {
> > >                 if (smt) {
> > > -                       i = select_idle_core(p, cpu, cpus, &idle_cpu);
> > > -                       if ((unsigned int)i < nr_cpumask_bits)
> > > -                               return i;
> > > +                       idle_cpu = select_idle_core(p, cpu, cpus, &idle_cpu);
> >
> > but how do you differentiate idle core (return value) and an idle cpu
> > in the core set in &idle_cpu
> >
> > You will return as soon as a cpu is idle and before testing all cores
> >
>
> Bah, I'm sorry, I was context switching between multiple tasks and failed
> to engage brain. I'll apply your hunk and resend. I don't think this

That's also happen to me

> merits retesting as the saving of avoiding the intermeriate is marginal.

I agree. You can add my Reviewed-by

>
> --
> Mel Gorman
> SUSE Labs