linux-kernel - Re: [PATCH v3 3/3] [RFC] CPUFreq: Add support for cpu-perf-dependencies

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Date:   Fri, 6 Nov 2020 16:25:14 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     Nicola Mazzucato <nicola.mazzucato@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, vireshk@...nel.org,
        robh+dt@...nel.org, sboyd@...nel.org, nm@...com,
        daniel.lezcano@...aro.org, morten.rasmussen@....com,
        chris.redpath@....com
Subject: Re: [PATCH v3 3/3] [RFC] CPUFreq: Add support for
 cpu-perf-dependencies

On 06-11-20, 10:37, Lukasz Luba wrote:
> Good question.
> 
> How about a different interface for those cpufreq drivers?
> That new registration API would allow to specify the cpumask.
> Or rely on EM cpumask: em_span_cpus(em)
> 
> Currently we have two ways to register cooling device:
> 1. when the cpufreq driver set a flag CPUFREQ_IS_COOLING_DEV, the core
> will register cooling device
> 2. cpufreq driver can explicitly call the registration function:
> cpufreq_cooling_register() with 'policy' as argument
> 
> That would need substantial change to the cpufreq cooling code, from
> policy oriented to custom driver's cpumask (like EM registration).

I am even wondering if we should really make that change. Why do we
need the combined load of the CPUs to be sent back to the IPA governor
? Why shouldn't they all do that (they == cdev) ?

This is a bit confusing to me, sorry about that. The cpufreq governors
take a look at all the CPUs utilization and set the frequency based on
the highest utilization (and not the total util).

While in this case we present the total load of the CPUs to the IPA
(based on the current frequency of the CPUs), in response to which it
tells us the frequency at which all the CPUs of the policy can run at
(I am not even sure if it is the right thing to do as the CPUs have
different loads). And how do we fit this dependent_cpus thing into
this.

Sorry, I am not sure what's the right way of doing thing here.

-- 
viresh