linux-kernel - Re: [PATCH v3 2/6] drivers/cpufreq: implement init_cpu_capacity

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Date:	Tue, 9 Feb 2016 15:54:50 +0000
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Juri Lelli <juri.lelli@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LAK <linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Sudeep Holla <sudeep.holla@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Mark Brown <broonie@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH v3 2/6] drivers/cpufreq: implement
 init_cpu_capacity_default()

On 05/02/16 09:30, Juri Lelli wrote:
> On 04/02/16 16:46, Vincent Guittot wrote:
>> On 4 February 2016 at 16:44, Vincent Guittot <vincent.guittot@...aro.org> wrote:
>>> On 4 February 2016 at 15:13, Juri Lelli <juri.lelli@....com> wrote:
>>>> On 04/02/16 13:35, Vincent Guittot wrote:
>>>>> On 4 February 2016 at 13:16, Juri Lelli <juri.lelli@....com> wrote:
>>>>>> Hi Vincent,
>>>>>>
>>>>>> On 04/02/16 13:03, Vincent Guittot wrote:
>>>>>>> On 4 February 2016 at 10:36, Morten Rasmussen <morten.rasmussen@....com> wrote:
>>>>>>>> On Wed, Feb 03, 2016 at 10:04:37PM +0100, Vincent Guittot wrote:
>>>>>>>>> On 3 February 2016 at 12:59, Juri Lelli <juri.lelli@....com> wrote:

[...]

>>>
>>> AFAICT, They don't have a dedicated cpufreq driver.
>>>
>>> More generally speaking, it can take time before having
>>
>> email sent before the ne d of the sentence ...
>>
>> More generally speaking, it can take time before having a cpufreq
>> driver whereas we want to run and test scheduler behavior of these
>> heterogenous platform
>>
> 
> I'm not familiar with this platform, but from what you are saying and
> what I could find online, it looks like full Linux support is not
> finished yet. Can we consider that as still in development? And if we
> can do that, maybe is fair enough that we use the sysfs interface to
> play with that platform until support is complete.
> 
> Do others have any opinion on this point?

IMHO, the solution should work for all of heterogeneous systems, (a) w/
cpufreq and driver, (b) w/ cpufreq and no driver loaded (yet) or (c) w/o
cpufreq.

That means that you can't put the benchmarking only into
cpufreq_register_driver() and rely on cpufreq policy topology.

Maybe you could do this for (b) and (c) inside an initcall and use
topology_core_cpumask() to figure out which cpu to profile?

This would then happen w/ the cpu frequency set by the fw.

But this then has to be synchronized somehow with the benchmarking
approach in cpufreq_register_driver().

[...]