linux-kernel - Re: [PATCH v3 1/6] cpufreq: schedutil: reset sg

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Date:   Thu, 30 Nov 2017 14:12:22 +0100
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, 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>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [PATCH v3 1/6] cpufreq: schedutil: reset sg_cpus's flags at IDLE
 enter

Hi,

On 30/11/17 11:47, Patrick Bellasi wrote:

[...]

> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 2f52ec0f1539..67339ccb5595 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -347,6 +347,12 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>  
>  	sg_cpu->util = util;
>  	sg_cpu->max = max;
> +
> +	/* CPU is entering IDLE, reset flags without triggering an update */
> +	if (unlikely(flags & SCHED_CPUFREQ_IDLE)) {
> +		sg_cpu->flags = 0;
> +		goto done;
> +	}

Looks good for now. I'm just thinking that we will happen for DL, as a
CPU that still "has" a sleeping task is not going to be really idle
until the 0-lag time. I guess we could move this at that point in time?

>  	sg_cpu->flags = flags;
>  
>  	sugov_set_iowait_boost(sg_cpu, time, flags);
> @@ -361,6 +367,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>  		sugov_update_commit(sg_policy, time, next_f);
>  	}
>  
> +done:
>  	raw_spin_unlock(&sg_policy->update_lock);
>  }
>  
> diff --git a/kernel/sched/idle_task.c b/kernel/sched/idle_task.c
> index d518664cce4f..6e8ae2aa7a13 100644
> --- a/kernel/sched/idle_task.c
> +++ b/kernel/sched/idle_task.c
> @@ -30,6 +30,10 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
>  	put_prev_task(rq, prev);
>  	update_idle_core(rq);
>  	schedstat_inc(rq->sched_goidle);
> +
> +	/* kick cpufreq (see the comment in kernel/sched/sched.h). */
> +	cpufreq_update_util(rq, SCHED_CPUFREQ_IDLE);

Don't know if it make things any cleaner, but you could add to the
comment that we don't actually trigger a frequency update with this
call.

Best,

Juri