linux-kernel - Re: [PATCH 5/6] cpufreq: Support for fast frequency switching

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Date:	Thu, 3 Mar 2016 21:56:40 +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>
Subject: Re: [PATCH 5/6] cpufreq: Support for fast frequency switching

On Thu, Mar 3, 2016 at 12:16 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Mar 02, 2016 at 03:12:33AM +0100, Rafael J. Wysocki wrote:
>> The most important change from the previous version is that the
>> ->fast_switch() callback takes an additional "relation" argument
>> and now the governor can use it to choose a selection method.
>
>> +unsigned int acpi_cpufreq_fast_switch(struct cpufreq_policy *policy,
>> +                                   unsigned int target_freq,
>> +                                   unsigned int relation)
>
> Would it make sense to replace the {target_freq, relation} pair with
> something like the CPPC {min_freq, max_freq} pair?

Yes, it would in general, but since I use __cpufreq_driver_target() in
the "slow driver" case, that would need to be reworked too for
consistency.  So I'd prefer to do that later.

> Then you could use the closest frequency to max provided it is larger
> than min.
>
> This communicates more actual information in the same number of
> parameters and would thereby allow for a more flexible (better)
> frequency selection.

Agreed.