linux-kernel - Re: [PATCH v6 3/3] sched/fair: Combine EAS check with overutilized access

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Message-ID: <CAKfTPtBTUHv3xBe0U75_4GGYPLYj-NC1uSGd6QjdQyS5k1N0QA@mail.gmail.com>
Date: Tue, 26 Mar 2024 09:26:25 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, peterz@...radead.org, yu.c.chen@...el.com, 
	dietmar.eggemann@....com, linux-kernel@...r.kernel.org, nysal@...ux.ibm.com, 
	aboorvad@...ux.ibm.com, srikar@...ux.ibm.com, vschneid@...hat.com, 
	pierre.gondois@....com, qyousef@...alina.io
Subject: Re: [PATCH v6 3/3] sched/fair: Combine EAS check with overutilized access

On Tue, 26 Mar 2024 at 08:58, Ingo Molnar <mingo@...nel.org> wrote:
>
>
> * Shrikanth Hegde <sshegde@...ux.ibm.com> wrote:
>
> >  /*
> > - * Ensure that caller can do EAS. overutilized value
> > - * make sense only if EAS is enabled
> > + * overutilized value make sense only if EAS is enabled
> >   */
> > -static inline int is_rd_overutilized(struct root_domain *rd)
> > +static inline int is_rd_not_overutilized(struct root_domain *rd)
> >  {
> > -     return READ_ONCE(rd->overutilized);
> > +     return sched_energy_enabled() && !READ_ONCE(rd->overutilized);
> >  }
>
> While adding the sched_energy_enabled() condition looks OK, the _not prefix
> This is silly: putting logical operators into functions names is far less
> readable than a !fn()...
>
> > -     if (!is_rd_overutilized(rq->rd) && cpu_overutilized(rq->cpu))
> > +     if (is_rd_not_overutilized(rq->rd) && cpu_overutilized(rq->cpu))
>
> Especially since we already have cpu_overutilized(). It's far more coherent
> to have the same basic attribute functions and put any negation into
> *actual* logical operators.

I was concerned by the || in this case that could defeat the purpose
of sched_energy_enabled() but it will return early anyway

return !sched_energy_enabled() || READ_ONCE(rd->overutilized);

>
> Thanks,
>
>         Ingo