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

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Date:	Thu, 4 Feb 2016 16:46:17 +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 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:
>>> >>
>>> >> [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.
>>>
>>
>> Sorry, can you make some examples so that I'm sure I understand what you
>> are referring to?
>
> As an example, the uniphier arm64 Soc doesn't have a cpufreq driver so far
>
>>
>> Anyway, don't these platform still make use of cpufreq (even if without
>> an OPP table) so that we can still control policy->max and min?
>
> 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

Thanks,
Vincent
>
>>
>> Thanks,
>>
>> - Juri