linux-kernel - Re: [PATCH 0/4] CPUFreq statistics retrieved by drivers

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Message-ID: <20200730085333.qubrsv7ufqninihd@vireshk-mac-ubuntu>
Date:   Thu, 30 Jul 2020 14:23:33 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org, sudeep.holla@....com,
        cristian.marussi@....com, rjw@...ysocki.net
Subject: Re: [PATCH 0/4] CPUFreq statistics retrieved by drivers

On 29-07-20, 16:12, Lukasz Luba wrote:
> The existing CPUFreq framework does not tracks the statistics when the
> 'fast switch' is used or when firmware changes the frequency independently
> due to e.g. thermal reasons. However, the firmware might track the frequency
> changes and expose this to the kernel.
> 
> This patch set aims to introduce CPUfreq statistics gathered by firmware
> and retrieved by CPUFreq driver. It would require a new API functions
> in the CPUFreq, which allows to poke drivers to get these stats.
> 
> The needed CPUFreq infrastructure is in patch 1/4, patch 2/4 extends
> ARM SCMI protocol layer, patches 3/4, 4/4  modify ARM SCMI CPUFreq driver.

Are you doing this for the fast switch case or because your platform
actually runs at frequencies which may be different from what cpufreq
core has requested ?

I am also not sure what these tables should represent, what the
cpufreq core has decided for the CPUs or the frequencies we actually
run at, as these two can be very different for example if the hardware
runs at frequencies which don't match exactly to what is there in the
freq table. I believe these are rather to show what cpufreq and its
governors are doing with the CPUs.

Over that I would like the userspace stats to work exactly as the way
they work right now, i.e. capture all transitions from one freq to
other, not just time-in-state. Also resetting of the stats from
userspace for example. All allocation and printing of the data must be
done from stats core, the only thing which the driver would do at the
end is updating the stats structure and nothing more. Instead of
reading all stats from the firmware, it will be much easier if you can
just get the information from the firmware whenever there is a
frequency switch and then we can update the stats the way it is done
right now. And that would be simple.

-- 
viresh