linux-kernel - Re: [PATCH 0/4] CPUFreq: Implement per policy instances of governors

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Date:	Mon, 4 Feb 2013 18:55:25 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Borislav Petkov <bp@...en8.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linaro-dev@...ts.linaro.org, robin.randhawa@....com,
	Steve.Bannister@....com, Liviu.Dudau@....com
Subject: Re: [PATCH 0/4] CPUFreq: Implement per policy instances of governors

On 4 February 2013 18:34, Borislav Petkov <bp@...en8.de> wrote:
> On Mon, Feb 04, 2013 at 06:24:19PM +0530, Viresh Kumar wrote:

>> What i believe is, the place where this directory was present earlier
>> (cpu/cpufreq/) wasn't the right place. Everything else was in cpu/cpu*/cpufreq,
>> then why this in cpu/cpufreq/ ?
>
> For the simple reason that the "cpu*" stuff is per-cpu - the
> "cpu/cpufreq" is per system, i.e. one governor for the whole system.

That's not completely true. There lies cpufreq directory in cpu/cpu*/ too,
where we have per policy stuff in cpu/cpu*/, like policy tunables and stats.
And the same is true for governor too.

>> I don't know how much of a pain it would be to fix userspace for it,
>> but i know it wouldn't be that small.
>
> I wouldn't fix userspace but simply not touch it. You can add your
> per-policy stuff in "cpu/cpu*" as new sysfs nodes and no need to
> change anything.

That was slightly confusing to me :(
The whole governor directory is per policy, i have to keep that in
cpu/cpu*/cpufreq
instead of cpu/cpufreq .

> And, also, as I suggested earlier, you should make it
> configurable since this code wouldn't make sense on x86, for example,
> where one system-wide governor should suffice.

Its not only for multicluster system, but a system where multiple cpus have
separate clock control and hence multiple policy structures.

>> I had another idea of doing this only for platforms where we have
>> multiple struct policy alive at the same time. But didn't wanted to
>> implement it before discussing this further.
>
> Simply put it behind a config option like
> CONFIG_CPU_IDLE_MULTIPLE_DRIVERS, call the whole menu
> "Multi-power-domain-policy" something and that should be modulary
> enough.

Problem with this is it would fail for single image solutions on which everybody
is working on. So, with multiple platforms compiled into a single
image, this wouldn't
work.
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