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

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Message-ID: <20170308041823.GB4526@vireshk-i7>
Date:   Wed, 8 Mar 2017 09:48:23 +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 07-03-17, 14:19, Rafael J. Wysocki wrote:
> On Tue, Mar 7, 2017 at 11:31 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > 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.
> 
> Well, yes, but if the current CPU has that flag set already, we surely
> don't need to check the other ones in the policy?

That's true for every other CPU in policy too..

> >> 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.
> 
> So why do you think it needs to be changed, but really?
> 
> Is that because it is particularly hard to follow or similar?

Just that I didn't like keeping the same code at two places (outside
and inside the loop) and the benefit it has.

Anyway, its not straight forward to get any numbers supporting my
argument. I can claim improvement only theoretically by comparing the
number of comparisons that we may end up doing for quad or octa core
policies. Lets abandon this patch as I failed to convince you :)

Thanks for applying the other two patches though.

Cheers.

-- 
viresh