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

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Message-ID: <CAKfTPtDVasamRtG2kLxP0HsohmVQTPrXRgx36e+jb3gozDoo6g@mail.gmail.com>
Date:	Thu, 4 Feb 2016 13:35:35 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Juri Lelli <juri.lelli@....com>
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>,
	Dietmar Eggemann <dietmar.eggemann@....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 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:
>>
>> [snip]
>>
>> >> > diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
>> >> > index 9e63fb1..c4025fd 100644
>> >> > --- a/drivers/cpufreq/Makefile
>> >> > +++ b/drivers/cpufreq/Makefile
>> >> > @@ -1,5 +1,5 @@
>> >> >  # CPUfreq core
>> >> > -obj-$(CONFIG_CPU_FREQ)                 += cpufreq.o freq_table.o
>> >> > +obj-$(CONFIG_CPU_FREQ)                 += cpufreq.o freq_table.o cpufreq_capacity.o
>> >>
>> >> Do you really want to have the calibration of capacity dependent of
>> >> cpufreq ? It means that we can't use it without a cpufreq driver.
>> >> IMHO, this creates a unnecessary dependency. I understand that you
>> >> must ensure that core runs at max fequency if a driver is present but
>> >> you should be able to calibrate the capacity if cpufreq is not
>> >> available but you have different capacity because micro architecture
>> >
>> > We could remove the dependency on cpufreq, but it would make things more
>> > complicated for systems which do have frequency scaling as we would have
>> > to either:
>> >
>> > 1) Run the calibration again once cpufreq has been initialized.
>>
>> or wait and let time for a driver to initialize and trig the
>> calibration. If calibration has not been done at the end of the boot,
>> you can force a calibration. If the cpufeq driver is a module and is
>> loaded far later for any good or bad reason, we will have to run the
>> calibration once again but at least the capacity will reflect he
>> current capacity of the CPUs.
>> I'm mainly worried that the compilation of the calibration is
>> dependent of CONFIG_CPU_FREQ not that cpufreq can trig the calibration
>> sequence
>>
>
> Yes, I guess we can make this work in some way. Out of curiosity,
> though, are out there heterogenous platforms that don't use cpufreq?

At least, you can find several heterogeneous platforms without OPP
table for CPUs in the kernel. That's probably a temporary situation
but which can become a permanent one. It means that we can't calibrate
the CPUs for these platforms.

Thanks,
Vincent

> I mean, I wouldn't add code and complexity from start, if there are not
> good reasons to do so.
>
> Thanks,
>
> - Juri