linux-kernel - Re: [RFC v2 0/3][TESTS] LAB: Support for Legacy Application Booster governor

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Message-ID: <76114024.UaPHgm94jK@vostro.rjw.lan>
Date:	Tue, 28 May 2013 23:48:14 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Lukasz Majewski <l.majewski@...sung.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	Jonghwa Lee <jonghwa3.lee@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Vicent Guittot <vincent.guittot@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	MyungJoo Ham <myungjoo.ham@...sung.com>,
	Lukasz Majewski <l.majewski@...ess.pl>
Subject: Re: [RFC v2 0/3][TESTS] LAB: Support for Legacy Application Booster governor - tests results

On Tuesday, May 28, 2013 03:26:25 PM Lukasz Majewski wrote:
> Hi Viresh, Rafael,
> 
> > On Tuesday, May 28, 2013 03:14:26 PM Viresh Kumar wrote:
> > > On 28 May 2013 12:10, Lukasz Majewski <l.majewski@...sung.com>
> > > wrote:
> > > > On 27 May 2013 17:30, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > > <manually added by viresh>
> > > >> On Monday, May 27, 2013 06:54:49 PM Viresh Kumar wrote:
> > > >> > On 27 May 2013 17:30, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > >> I was talking about /sys/devices/system/cpu/cpufreq/boost that
> > > >> appears to have been added by commit 615b730 (acpi-cpufreq: Add
> > > >> support for disabling dynamic overclocking).
> > > >>
> > > >> That's in acpi-cpufreq, but since that setting seems to be
> > > >> generally useful, it may be a good idea to move it to the core
> > > >> somehow.
> > > 
> > > Problem is in breaking existing cpufreq userspace for this driver.
> > > Is this allowed?
> > > 
> > > > I think that Viresh wanted to add "boost" option to
> > > > /sys/devices/system/cpu/cpuX/cpufreq/ to be able to control boost
> > > > at separate cores (policies).
> > > >
> > > > The localization, which you have proposed:
> > > > /sys/devices/system/cpu/cpufreq/boost
> > > >
> > > > implies, that boost is a global feature (enabled for all cores
> > > > and for all available policies).
> > > >
> > > > Which approach shall be used then?
> > > 
> > > We can use: get_governor_parent_kobj() to get the best location
> > > for boost. But I had some other issues in mind:
> > > - boost is governor dependent.. i.e. It is only required for
> > > ondemand governor (And LAB if it makes it to mainline :) ).. Other
> > > governors doesn't need it. So, it would be better to add it in
> > > governor's directory.
> > 
> 
> 
> > I'm not sure about that.  On x86 boost will be used with all
> > governors if enabled (as currently defined in acpi-cpufreq).
> 
> All governors can benefit from the overclocking code.
> 
> 
> > 
> > Also it looks like this depends on the driver too, because if the
> > driver doesn't have "turbo" frequencies, the governor won't be able
> > use "turbo" anyway.
> > 
> 
> Rafael is correct here. The overclocking framework depends on
> cpufreq_driver (exynos-cpufreq in my case) to switch to overclocked
> frequency.
> 
> 
> > > - This will break existing users of acpi-cpufreq driver.
> > > 
> > > @Rafael: Please suggest what to do here.
> > 
> > So first, it would make sense to use a per-driver "boost" attribute
> > indicating whether or not the given driver should present any "turbo"
> > frequencies to the governor.
> 
> Now I'm using a device tree's cpufreq section (defined at
> exynos4412-redwood.dts) with overclocking = "okay" attribute defined.
> Then, on this basis, we could decide at cpufreq init time if we will
> export any overclocking related sysfs entries (or init overclocking at
> all). It would assure clearer code.

Well, what about users?  Don't you want them to be able to decide whether
or not to use "turbo"?

> >  That'd work along the lines of the
> > acpi-cpufreq "boost", but I don't think that the global_boost
> > attribute should be created by the driver (it'd be better if the
> > driver provided methods to the core for handling that).
> 
> I think that global cpufreq device tree attribute shall be defined.

What do you mean by "device tree attribute"?  If you mean FDTs as used by
ARM for system configuration description, that wouldn't be portable, because
DTs aren't used for that on the (majority of) x86 systems.

> The overclocking will be an integral part of the cpufreq framework.

Well, to be precise, I was thinking about moving the management of the
/sys/devices/system/cpu/cpufreq/boost attribute from acpi-cpufreq to the
code so that other drivers may use it too.  Does that make sense to you?

> > 
> > Second, I'm not sure if an additional knob for the governor is
> > necessary.  It may just use the turbo frequencies if available (and
> > if the governor cannot use them, it simply won't use them).
> 
> I cannot agree. It is welcome to be able to enable/disable the feature
> when needed. Turbo frequencies shall not be "available" for use all the
> time.

Well, they won't.  The "boost" attribute above may be used to turn "turbo"
off in that case.  I'm not sure why one more attribute is needed here.

Can you please explain how you the whole mechanism is supposed to work on
your platform, in general terms?

Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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