linux-kernel - Re: [PATCH 2/2] thermal: cpufreq_cooling: Reuse effective_cpu

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Date:   Thu, 22 Oct 2020 16:36:56 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Amit Kucheria <amit.kucheria@...durent.com>,
        linux-kernel@...r.kernel.org, Quentin Perret <qperret@...gle.com>,
        Rafael Wysocki <rjw@...ysocki.net>, linux-pm@...r.kernel.org,
        lukasz.luba@....com
Subject: Re: [PATCH 2/2] thermal: cpufreq_cooling: Reuse effective_cpu_util()

On 22-10-20, 11:05, Peter Zijlstra wrote:
> On Thu, Oct 22, 2020 at 02:02:55PM +0530, Viresh Kumar wrote:
> > One of the issues I see with this is that schedutil may not be
> > available in all configurations and it is still absolutely fine to
> > using the suggested helper to get the energy numbers in such cases, so
> > we shouldn't really make it scheutil dependent.
> 
> The only constraint on schedutil is SMP I think; aside from that it
> should/could always be available.
> 
> Given the trainwreck here:
> 
>   20201022071145.GM2628@...ez.programming.kicks-ass.net
> 
> (you're on Cc), I'm starting to lean more and more towards making it
> unconditionally available (when SMP).
> 
> Anybody forcing it off either sets performance (in which case we don't
> care about energy usage anyway)

I agree.

> or they select one of the old (broken)
> ondemand/conservative things and I don't give a crap.

The other kernel layers, for example cpufreq-cooling in question here,
don't really need to bother with the governor in use and should be
able to get the energy numbers anyway. So for me, the energy number
that the cpufreq-cooling stuff gets should be same irrespective of the
governor in use, schedutil or ondemand.

Having said that, schedutil really doesn't need to install the
fallback (which you suggested earlier), rather the scheduler core can
do that directly with cpufreq core and schedutil can also use the same
fallback mechanism maybe ? And so we can avoid the exporting of stuff
that way.

-- 
viresh