linux-kernel - Re: [Eas-dev] [PATCH V3 1/3] sched: cpufreq: Allow remote cpufreq callbacks

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Date:   Fri, 28 Jul 2017 11:30:54 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Saravana Kannan <skannan@...eaurora.org>
Cc:     eas-dev@...ts.linaro.org, linux-pm@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        smuckle.linux@...il.com, Len Brown <lenb@...nel.org>
Subject: Re: [Eas-dev] [PATCH V3 1/3] sched: cpufreq: Allow remote cpufreq
 callbacks

On 27-07-17, 12:55, Saravana Kannan wrote:
> Yes. Simplifying isn't always about number of lines of code. It's also about
> abstraction. Having generic scheduler code care about HW details doesn't
> seem nice.

I can argue that even the policy->cpus field is also hardware
specific, isn't it ? And we are using that in the schedutil governor
anyway. What's wrong with having another field (in a generic way) in
the same structure that tells us more about hardware ?

And then schedutil isn't really scheduler, but a cpufreq governor.
Just like ondemand/conservative, which are also called from the same
scheduler path.

> It'll literally one simple check (cpu == smp_processor_id()) or (cpu "in"
> policy->cpus).
> 
> Also, this is only for drivers that currently support fast switching. How
> many of those do you have?

Why? Why shouldn't we do that for the other drivers? I think it should
be done across everyone.

> >The core already has most of the data required and I believe that we
> >need to handle it in the governor's code as is handled in this series.
> 
> Clearly, it doesn't. You are just making assumptions about HW.

So assuming that any CPU from a policy can change freq on behalf of
all the CPUs of the same policy is wrong? That is the basis of how the
cpufreq core is designed.

-- 
viresh