linux-kernel - Re: [PATCH v3 1/7][Resend] cpufreq: Rework the scheduler hooks for triggering updates

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Date:	Wed, 9 Mar 2016 15:02:41 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3 1/7][Resend] cpufreq: Rework the scheduler hooks for
 triggering updates

On Wed, Mar 9, 2016 at 2:41 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Mar 08, 2016 at 03:25:16AM +0100, Rafael J. Wysocki wrote:
>> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>
>> Commit fe7034338ba0 (cpufreq: Add mechanism for registering
>> utilization update callbacks) added cpufreq_update_util() to be
>> called by the scheduler (from the CFS part) on utilization updates.
>> The goal was to allow CFS to pass utilization information to cpufreq
>> and to trigger it to evaluate the frequency/voltage configuration
>> (P-state) of every CPU on a regular basis.
>>
>> However, the last two arguments of that function are never used by
>> the current code, so CFS might simply call cpufreq_trigger_update()
>> instead of it (like the RT and DL sched classes).
>>
>> For this reason, drop the last two arguments of cpufreq_update_util(),
>> rename it to cpufreq_trigger_update() and modify CFS to call it.
>>
>> Moreover, since the utilization is not involved in that now, rename
>> data types, functions and variables related to cpufreq_trigger_update()
>> to reflect that (eg. struct update_util_data becomes struct
>> freq_update_hook and so on).
>
>> -void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
>> +void cpufreq_trigger_update(u64 time)
>
> So I'm not convinced about this. Yes the utility of this function is
> twofold. One to allow in-situ frequency adjustments where possible, but
> two, also very much to allow using the statistics already gathered.
>
> Sure, 4.5 will not have any such users, but who cares.
>
> And I'm really not too worried about 'random' people suddenly using it
> to base work on. Either people are already participating in these
> discussions and will thus be aware of whatever concerns there might be,
> or we'll tell them when they post their code.
>
> And when they don't participate and don't post their code, I really
> don't care about them anyway :-)

OK