linux-kernel - Re: [PATCH 2/2] sched/uclamp: Fix iowait boost escaping uclamp restriction

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Date:   Fri, 17 Dec 2021 16:56:33 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Qais Yousef <qais.yousef@....com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Beata Michalska <Beata.Michalska@....com>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] sched/uclamp: Fix iowait boost escaping uclamp restriction

On Thu, Dec 16, 2021 at 11:53 PM Qais Yousef <qais.yousef@....com> wrote:
>
> iowait_boost signal is applied independently of util and doesn't take
> into account uclamp settings of the rq. An io heavy task that is capped
> by uclamp_max could still request higher frequency because
> sugov_iowait_apply() doesn't clamp the boost via uclamp_rq_util_with()
> like effective_cpu_util() does.
>
> Make sure that iowait_boost honours uclamp requests by calling
> uclamp_rq_util_with() when applying the boost.
>
> Fixes: 982d9cdc22c9 ("sched/cpufreq, sched/uclamp: Add clamps for FAIR and RT tasks")
> Signed-off-by: Qais Yousef <qais.yousef@....com>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  kernel/sched/cpufreq_schedutil.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> index 48327970552a..93dcea233c65 100644
> --- a/kernel/sched/cpufreq_schedutil.c
> +++ b/kernel/sched/cpufreq_schedutil.c
> @@ -289,6 +289,7 @@ static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time)
>          * into the same scale so we can compare.
>          */
>         boost = (sg_cpu->iowait_boost * sg_cpu->max) >> SCHED_CAPACITY_SHIFT;
> +       boost = uclamp_rq_util_with(cpu_rq(sg_cpu->cpu), boost, NULL);
>         if (sg_cpu->util < boost)
>                 sg_cpu->util = boost;
>  }
> --
> 2.25.1
>