linux-kernel - Re: [PATCH v3 1/3] sched/fair: add util

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Date:   Wed, 24 Jan 2018 08:40:07 -0800
From:   Joel Fernandes <joelaf@...gle.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Paul Turner <pjt@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Todd Kjos <tkjos@...roid.com>,
        Steve Muckle <smuckle@...gle.com>
Subject: Re: [PATCH v3 1/3] sched/fair: add util_est on top of PELT

On Tue, Jan 23, 2018 at 10:08 AM, Patrick Bellasi
<patrick.bellasi@....com> wrote:
> The util_avg signal computed by PELT is too variable for some use-cases.
> For example, a big task waking up after a long sleep period will have its
> utilization almost completely decayed. This introduces some latency before
> schedutil will be able to pick the best frequency to run a task.
[...]
> -static inline unsigned long task_util(struct task_struct *p);
>  static unsigned long cpu_util_wake(int cpu, struct task_struct *p);
>
>  static unsigned long capacity_spare_wake(int cpu, struct task_struct *p)
> @@ -6262,6 +6337,11 @@ static inline unsigned long task_util(struct task_struct *p)
>         return p->se.avg.util_avg;
>  }
>
> +static inline unsigned long task_util_est(struct task_struct *p)
> +{
> +       return max(p->se.avg.util_est.ewma, p->se.avg.util_est.last);
> +}
> +
>  /*
>   * cpu_util_wake: Compute cpu utilization with any contributions from
>   * the waking task p removed.
> diff --git a/kernel/sched/features.h b/kernel/sched/features.h
> index 9552fd5854bf..c459a4b61544 100644
> --- a/kernel/sched/features.h
> +++ b/kernel/sched/features.h
> @@ -85,3 +85,8 @@ SCHED_FEAT(ATTACH_AGE_LOAD, true)
>  SCHED_FEAT(WA_IDLE, true)
>  SCHED_FEAT(WA_WEIGHT, true)
>  SCHED_FEAT(WA_BIAS, true)
> +
> +/*
> + * UtilEstimation. Use estimated CPU utilization.
> + */
> +SCHED_FEAT(UTIL_EST, false)
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 2e95505e23c6..0b4d9750a927 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -470,6 +470,7 @@ struct cfs_rq {
>          * CFS load tracking
>          */
>         struct sched_avg avg;
> +       unsigned long util_est_runnable;

Since struct sched_avg would now have util_est, cfs_rq gets it too.
Then can we not try to reuse that struct and avoid having to expand
cfs_rq more than needed?

I went through previous conversations and couldn't find a reason, if I
missed something I appreciate if you can explain the rationale.

thanks,

- Joel