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

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Message-ID: <20210222163947.GB225035@e124901.cambridge.arm.com>
Date:   Mon, 22 Feb 2021 16:39:47 +0000
From:   Vincent Donnefort <vincent.donnefort@....com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, 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 Mon, Feb 22, 2021 at 04:23:42PM +0000, 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?

You preempted my previous email :)

Yeah, that looks like what we want, I'll give a try.

Thanks,

-- 
Vincent.

> 
> 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);
>                 struct task_struct *tsk = cpu == dst_cpu ? p : NULL;
> +               unsigned long cpu_util;
> +
> +               if (cpu == dst_cpu)
> +                       util_running += task_util_est();
> 
>                 /*
>                  * Busy time computation: utilization clamping is not
> @@ -6543,7 +6548,7 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
>                  * is already enough to scale the EM reported power
>                  * consumption at the (eventually clamped) cpu_capacity.
>                  */
> -               sum_util += schedutil_cpu_util(cpu, util_cfs, cpu_cap,
> +               sum_util += schedutil_cpu_util(cpu, util_running, cpu_cap,
>                                                ENERGY_UTIL, NULL);
> 
>                 /*
> @@ -6553,7 +6558,7 @@ compute_energy(struct task_struct *p, int dst_cpu, struct perf_domain *pd)
>                  * NOTE: in case RT tasks are running, by default the
>                  * FREQUENCY_UTIL's utilization can be max OPP.
>                  */
> -               cpu_util = schedutil_cpu_util(cpu, util_cfs, cpu_cap,
> +               cpu_util = schedutil_cpu_util(cpu, util_freq, cpu_cap,
>                                               FREQUENCY_UTIL, tsk);
>                 max_util = max(max_util, cpu_util);
>         }
>