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

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Date:	Wed, 29 May 2013 10:53:19 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Lukasz Majewski <l.majewski@...sung.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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 29 May 2013 03:18, Rafael J. Wysocki <rjw@...k.pl> wrote:
> 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:

>> > 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.

Yeah.

>> > 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.

Yes.

>> > 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.

@Lukasz: So, you need to add another field in struct cpufreq_driver,
which will be called "turbo_mode" or something better.

>> 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"?

I believe Lukasz was saying that we can have two levels of enabling it..
Firstly the driver can say if it supports turbo_mode or not and so will
register cpufreq_driver with appropriate parameters..

Now if turbo_mode == true, then sysfs entry will be created by cpufreq
core which users can enable/disable...

And this is what I had in mind too.

>> 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.

So, drivers should pass correct value in boost_mode in struct cpufreq_driver.
They get it from DT or is hard coded doesn't matter at all to the core. But
yes getting a single name for DT bindings would be good. We should use
the same name at that place too: turbo_mode

>> 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?

Obviously yes. The sysfs related code from acpi-cpufreq should be moved
to cpufreq.c and will be functional once cpufreq_driver has boost_mode set
as true.

>> > 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.

Yes, you can disable that from userspace once your driver said: "I support
turbo mode"..
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