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

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Message-ID: <CAJZ5v0i0AGZVEYgJzDRVJHqCjAGDXhCeQ4gJBn77z_5cCh2Mqg@mail.gmail.com>
Date:	Fri, 20 May 2016 02:37:17 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Steve Muckle <steve.muckle@...aro.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 2:24 AM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> 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.

Also I think that it would be good to avoid walking the frequency
table twice in case we end up wanting to update the frequency after
all.  With the [4/5] we'd do it once in get_next_freq() and then once
more in cpufreq_driver_fast_switch(), for example, and walking the
frequency table may be more expensive that doing the switch in the
first place.