Re: [PATCH v3 2/6] drivers/cpufreq: implement init_cpu_capacity_default()

[Juri Lelli <juri.lelli-5wv7dgnIgG8@public.gmane.org>]

Hi Vincent,

On 04/02/16 13:03, Vincent Guittot wrote:
> On 4 February 2016 at 10:36, Morten Rasmussen <morten.rasmussen-5wv7dgnIgG8@public.gmane.org> 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-5wv7dgnIgG8@public.gmane.org> 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?
I mean, I wouldn't add code and complexity from start, if there are not
good reasons to do so.

Thanks,

- Juri
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