linux-kernel - Re: [PATCH v3 3/6] cpufreq: schedutil: update CFS util only if used

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Message-ID: <20171214044523.GV3322@vireshk-i7>
Date:   Thu, 14 Dec 2017 10:15:23 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Juri Lelli <juri.lelli@...hat.com>, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>
Subject: Re: [PATCH v3 3/6] cpufreq: schedutil: update CFS util only if used

On 07-12-17, 14:19, Patrick Bellasi wrote:
> On 07-Dec 10:45, Viresh Kumar wrote:
> > On 30-11-17, 15:57, Patrick Bellasi wrote:
> > > Yes, that's a pretty trivial update with a confusing changelog.
> > > 
> > > If we think it's worth to keep (and correct as well) I'll update the
> > > commit message.
> > 
> > We also need to update the commit log based on feedback from Vikram on
> > V2. Which said that the utilization can't change around the lock here
> > as we are within rq lock section, though max can change (maybe). So
> > this patch only takes care of locking before reading max.

I have more doubts on the max reason as well. Max isn't protected by the
sg_policy lock of schedutil and it can change any time. So even after moving
code around with this patch, we wouldn't fix any race and so I am not sure this
patch helps at all. But, I have sent the same diff for another reason now in my
series. Maybe I should have kept you as the author of that patch, but I forgot.
Will do that if I need to send a V2.

> Ok, right... will do.
> 
> Thus you are still of the opinion to keep this patch in the series?

Yes, but we need a good reason for that :)

-- 
viresh