linux-kernel - Re: [PATCH 4/4] cpu_cooling: Drop static-power related stuff

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Date:   Wed, 22 Nov 2017 10:59:21 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Eduardo Valentin <edubezval@...il.com>
Cc:     Javi Merino <javi.merino@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Lukasz Luba <llu.ker.dev@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Punit Agrawal <punit.agrawal@....com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Zhang Rui <rui.zhang@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linux PM <linux-pm@...r.kernel.org>,
        Lukasz Luba <lukasz.luba@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] cpu_cooling: Drop static-power related stuff

(sorry for chiming in quite late)

On 21/11/17 18:12, Eduardo Valentin wrote:
> On Tue, Nov 21, 2017 at 06:00:07PM +0000, Javi Merino wrote:
>> Hi,
>>
>> On Tue, Nov 21, 2017 at 08:57:06AM -0800, Eduardo Valentin wrote:
>>

[...]

>>
>> In a nutshell, mainline does not want platform specific code, but we
>> haven't figured out how to calculate static power without platform
>> specific code.>
> To, that is still fine to have it as a callback, as long as you have at
> least one user! I still do not understand why Juno static power cannot
> go as platform code that register the callback to implement the static
> power model.
> 

1. It was proved not so useful(anyone can prove otherwise ?)
2. I am told static power is negligible compared to dynamic power with
   new fab processes.
3. It's very hard to even test IPA on Juno as it doesn't reach the
   required critical temperature easily. So as Juno platform maintainer
   I want a test case to test regression before we merge anything.

IMO, if the $subject code is expected to be used on Juno, then my answer
is no if one can't test it reliably and also prove that static power
really matters on Juno. So far, I have heard both the above is not
possible. So please delete the code if Juno is the only user in
short and mid term. We can get the code back if we find any users in
longer term.

-- 
Regards,
Sudeep