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

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Date:   Tue, 26 Apr 2022 08:41:26 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
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 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.

-- 
viresh