linux-kernel - Re: [PATCH 5/5] cpufreq: schedutil: do not update rate limit ts when freq is unchanged

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Date:	Fri, 20 May 2016 02:24:19 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 5/5] cpufreq: schedutil: do not update rate limit ts when
 freq is unchanged

On Fri, May 20, 2016 at 1:34 AM, Steve Muckle <steve.muckle@...aro.org> wrote:
> On Thu, May 19, 2016 at 11:15:52PM +0200, Rafael J. Wysocki wrote:
>> But anyway this change again seems to be an optimization that might be
>> done later to me.
>>
>> I guess there are many things that might be optimized in schedutil,
>> but I'd prefer to address one item at a time, maybe going after the
>> ones that appear most relevant first?
>
> Calling the last two patches in this series optimizations is a stretch
> IMO. Issuing frequency change requests that result in the same
> target-supported frequency is clearly unnecessary and ends up delaying
> more urgent frequency changes, which I think is more like a bug.

The [4/5] is pulling stuff where it doesn't belong.  Simple as that.
Frequency tables don't belong in schedutil, so don't pull them in
there.

If you want to do that cleanly, add a call to the driver that will
tell you what frequency would be selected by it if it were given a
particular target.

I actually do agree with the direction of it and the [5/5], but I
don't like cutting corners. :-)

> These patches are also needed in conjunction with the first three to address
> the remote wakeup delay.

Well, does this mean that without the [4-5/5] the rest of the series
doesn't provide as much benefit as initially expected?

> Are there specific items you want to see addressed before these patches could go in?

Do you mean in addition to what I already said in my comments?

> I'm aware of the RT/DL support that needs improving, though
> that should be orthogonal.
>
> Also if it helps, I can provide a test case and/or traces to show the
> need for the last two patches.

Yes, that will help.

Thanks,
Rafael