linux-kernel - Re: [PATCH] sched: move access of avg_rt and avg

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Message-ID: <CAKfTPtBYRT9oOoLwZ-Gg3KVdK+2iJnPaXaWfiuebnGEOOArH0Q@mail.gmail.com>
Date: Thu, 21 Dec 2023 17:16:38 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
Cc: mingo@...nel.org, peterz@...radead.org, dietmar.eggemann@....com, 
	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com, yu.c.chen@...el.com, 
	tim.c.chen@...ux.intel.com
Subject: Re: [PATCH] sched: move access of avg_rt and avg_dl into existing
 helper functions

Hi Shrikanth,

On Wed, 20 Dec 2023 at 15:49, Shrikanth Hegde
<sshegde@...ux.vnet.ibm.com> wrote:
>
>
>
> On 12/20/23 7:29 PM, Vincent Guittot wrote:
>
> Hi Vincent, thanks for taking a look.
>
> > On Wed, 20 Dec 2023 at 07:55, Shrikanth Hegde
> > <sshegde@...ux.vnet.ibm.com> wrote:
> >>

[...]

> >> -#ifdef CONFIG_HAVE_SCHED_AVG_IRQ
> >> -       if (READ_ONCE(rq->avg_irq.util_avg))
> >> +       if (cpu_util_irq(rq))
> >
> > cpu_util_irq doesn't call READ_ONCE()
> >
>
>
> I see. Actually it would be right if cpu_util_irq does call READ_ONCE no?

Yes, cpu_util_irq should call READ_ONCE()

>
> Sorry i havent yet understood the memory barriers in details. Please correct me
> if i am wrong here,
> since ___update_load_avg(&rq->avg_irq, 1) does use WRITE_ONCE and reading out this
> value using cpu_util_irq on a different CPU should use READ_ONCE no?

Yes

>
> >
> >>                 return true;
> >> -#endif
> >>
> >>         return false;
> >>  }
> >> @@ -9481,8 +9479,8 @@ static unsigned long scale_rt_capacity(int cpu)
> >>          * avg_thermal.load_avg tracks thermal pressure and the weighted
> >>          * average uses the actual delta max capacity(load).
> >>          */
> >> -       used = READ_ONCE(rq->avg_rt.util_avg);
> >> -       used += READ_ONCE(rq->avg_dl.util_avg);
> >> +       used = cpu_util_rt(rq);
> >> +       used += cpu_util_dl(rq);
> >>         used += thermal_load_avg(rq);
> >>
> >>         if (unlikely(used >= max))
> >> --
> >> 2.39.3
> >>