linux-kernel - Re: [PATCH] sched/fair: Fix task utilization accountability in cpu_util

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Message-ID: <c101892b-157c-0074-12cb-9651d1c4c4e6@arm.com>
Date:   Tue, 23 Feb 2021 15:47:42 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Quentin Perret <qperret@...gle.com>,
        Vincent Donnefort <vincent.donnefort@....com>
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, patrick.bellasi@...bug.net,
        valentin.schneider@....com
Subject: Re: [PATCH] sched/fair: Fix task utilization accountability in
 cpu_util_next()

On 22/02/2021 17:23, Quentin Perret wrote:
> On Monday 22 Feb 2021 at 15:58:56 (+0000), Quentin Perret wrote:
>> But in any case, if we're going to address this, I'm still not sure this
>> patch will be what we want. As per my first comment we need to keep the
>> frequency estimation right.
> 
> Totally untested, but I think in principle you would like something like
> the snippet below. Would that work?
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 04a3ce20da67..6594d875c6ac 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6534,8 +6534,13 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
>          * its pd list and will not be accounted by compute_energy().
>          */
>         for_each_cpu_and(cpu, pd_mask, cpu_online_mask) {
> -               unsigned long cpu_util, util_cfs = cpu_util_next(cpu, p, dst_cpu);
> +               unsigned long util_freq = cpu_util_next(cpu, p, dst_cpu);
> +               unsigned long util_running = cpu_util_without(cpu, p);

Wouldn't this be the same as:

                 unsigned long util_running = cpu_util_next(cpu, p, -1);

except some different handling of !last_update_time and
'task_on_rq_queued(p) || current == p)' in cpu_util_without() which
shouldn't happen in EAS.

We have quite a lot of util related functions!

[...]