linux-kernel - Re: [PATCH 3/3] cpufreq: schedutil: remove redundant code from sugov_next_freq

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Message-ID: <20170307103108.GA4526@vireshk-i7>
Date:   Tue, 7 Mar 2017 16:01:08 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH 3/3] cpufreq: schedutil: remove redundant code from
 sugov_next_freq_shared()

On 06-03-17, 13:24, Rafael J. Wysocki wrote:
> On Mon, Mar 6, 2017 at 5:45 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 04-03-17, 01:11, Rafael J. Wysocki wrote:
> >> So one idea is that if SCHED_CPUFREQ_RT_DL is set in flags, we don't even
> >> need to start the loop which is quite a cost to simply notice that there's
> >> nothing to do.
> >
> > Hmm. Isn't the probability of this flag being set, same for all CPUs in the
> > policy?
> 
> No, I don't think so.

Why do you think so? I thought all CPU in the policy can have the RT/DL flag set
and the probability of all of them is just the same.

> So to the point, the code was written this way on purpose and not just
> by accident as your changelog suggests and

I didn't wanted to convey that really and I knew that it was written on purpose.

> if you want to change it, you need numbers.

What kind of numbers can we get for such a change ? I tried to take the running
average of the time it takes to execute this routine over 10000 samples, but it
varies a lot even with the same build. Any tests like hackbench, etc wouldn't be
of any help as well.

-- 
viresh