linux-kernel - Re: [RFC PATCH v3 0/5] Introduce Cpufreq Active Stats

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Message-ID: <f6bb20c6-38a0-57d6-8979-d14e445da623@arm.com>
Date:   Tue, 26 Apr 2022 08:46:57 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
        rafael@...nel.org, daniel.lezcano@...aro.org, amitk@...nel.org,
        rui.zhang@...el.com, amit.kachhap@...il.com,
        linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH v3 0/5] Introduce Cpufreq Active Stats



On 4/26/22 04:11, Viresh Kumar wrote:
> On 06-04-22, 23:08, Lukasz Luba wrote:
>> Hi all,
>>
>> This is the 3rd version of patch set which tries to address issues which are
>> due to missing proper information about CPU performance in time.
>>
>> The issue description:
>> 1. "Cpufreq statistics cover the time when CPUs are in idle states, so they
>>     are not suitable for certain purposes, like thermal control." Rafael [2]
>> 2. Thermal governor Intelligent Power Allocation (IPA) has to estimate power,
>>     for the last period, e.g. 100ms, for each CPU in the Cluster, to grant new
>>     power and set max possible frequency. Currently in some cases it gets big
>>     error, when the frequency of CPU changed in the middle. It is due to the
>>     fact that IPA reads the current frequency for the CPU, not aware of all
>>     other frequencies which were actively (not in idle) used in the last 100ms.
>>
>> This code focuses on tracking the events of idle entry/exit for each CPU
>> and combine them with the frequency tracked statistics inside internal
>> statistics arrays (per-CPU). In the old cpufreq stats we have one shared
>> statistics array for the policy (all CPUs) and not take into account
>> periods when each CPU was in idle.
>>
>> Sometimes the IPA error between old estimation signal and reality is quite
>> big (>50%).
> 
> It would have been useful to show how the stats hierarchy looks in userspace
> now.
> 

I haven't modify your current cpufreq stats, they are still counting
total time (idle + running) for the given frequency. I think this is
still useful for some userspace tools. These new proposed stats don't
have such sysfs interface to read them. I don't know if userspace would
be interested in this information (the running only time). IIRC Android
uses bpf mechanisms to get this information to the userspace.