linux-kernel - Re: [PATCH 1/4] cpufreq: Add a cpufreq pressure feedback for the scheduler

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Message-ID: <CAJZ5v0gD-utGhM3vN7JmPia1CVcSQa6RPnk2xMBXXc6asRTn=g@mail.gmail.com>
Date:   Thu, 14 Dec 2023 10:40:28 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        catalin.marinas@....com, will@...nel.org, sudeep.holla@....com,
        rafael@...nel.org, agross@...nel.org, andersson@...nel.org,
        konrad.dybcio@...aro.org, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, rui.zhang@...el.com,
        mhiramat@...nel.org, daniel.lezcano@...aro.org,
        amit.kachhap@...il.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] cpufreq: Add a cpufreq pressure feedback for the scheduler

On Thu, Dec 14, 2023 at 10:07 AM Lukasz Luba <lukasz.luba@....com> wrote:
>
> On 12/14/23 07:57, Vincent Guittot wrote:
> > On Thu, 14 Dec 2023 at 06:43, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >>
> >> On 12-12-23, 15:27, Vincent Guittot wrote:
> >>> @@ -2618,6 +2663,9 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
> >>>        policy->max = __resolve_freq(policy, policy->max, CPUFREQ_RELATION_H);
> >>>        trace_cpu_frequency_limits(policy);
> >>>
> >>> +     cpus = policy->related_cpus;
> >>> +     cpufreq_update_pressure(cpus, policy->max);
> >>> +
> >>>        policy->cached_target_freq = UINT_MAX;
> >>
> >> One more question, why are you doing this from cpufreq_set_policy ? If
> >> due to cpufreq cooling or from userspace, we end up limiting the
> >> maximum possible frequency, will this routine always get called ?
> >
> > Yes, any update of a FREQ_QOS_MAX ends up calling cpufreq_set_policy()
> > to update the policy->max
> >
>
> Agree, cpufreq sysfs scaling_max_freq is also important to handle
> in this new design. Currently we don't reflect that as reduced CPU
> capacity in the scheduler. There was discussion when I proposed to feed
> that CPU frequency reduction into thermal_pressure [1].
>
> The same applies for the DTPM which is missing currently the proper
> impact to the CPU reduced capacity in the scheduler.
>
> IMHO any limit set into FREQ_QOS_MAX should be visible in this
> new design of capacity reduction signaling.
>
> [1] https://lore.kernel.org/lkml/20220930094821.31665-2-lukasz.luba@arm.com/

Actually, freq_qos_read_value(&policy->constraints, FREQ_QOS_MAX) will
return the requisite limit.