linux-kernel - Re: [PATCH] [RFC] sched: restrict iowait boost for boosted task only

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Message-ID: <20200126002515.gjpiiur565muruas@e107158-lin.cambridge.arm.com>
Date:   Sun, 26 Jan 2020 00:25:17 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Wei Wang <wvw@...gle.com>
Cc:     Valentin Schneider <valentin.schneider@....com>,
        Quentin Perret <qperret@...gle.com>,
        Wei Wang <wei.vince.wang@...il.com>, dietmar.eggemann@....com,
        chris.redpath@....com, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [RFC] sched: restrict iowait boost for boosted task only

On 01/25/20 23:59, Qais Yousef wrote:
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 9b8916fd00a2..a76c02eecdaf 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -421,7 +421,8 @@ static unsigned long sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
>          * into the same scale so we can compare.
>          */
>         boost = (sg_cpu->iowait_boost * max) >> SCHED_CAPACITY_SHIFT;
> -       return max(boost, util);
> +       boost = max(boost, util);
> +       return uclamp_util_with(cpu_rq(sg_cpu->cpu), boost, NULL);
>  }
> 
>  #ifdef CONFIG_NO_HZ_COMMON

Forgot to mention this will work if the background task is the only task
running on this CPU. Like Quentin already pointed out, the iowait_boost might
need more massaging to allow finer per task control.

--
Qais Yousef