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

[Rafael J. Wysocki]

On Thu, Dec 14, 2023 at 10:07 AM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
>
> On 12/14/23 07:57, Vincent Guittot wrote:
> > On Thu, 14 Dec 2023 at 06:43, Viresh Kumar <viresh.kumar@xxxxxxxxxx> 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@xxxxxxx/

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