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

[Lukasz Luba]

On 12/14/23 07:57, Vincent Guittot wrote:
> On Thu, 14 Dec 2023 at 06:43, Viresh Kumar <viresh.kumar at linaro.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/