linux-kernel - Re: [PATCH v6 6/7][Resend] cpufreq: Support for fast frequency switching

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Date:	Mon, 28 Mar 2016 09:47:53 -0700
From:	Steve Muckle <steve.muckle@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.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 v6 6/7][Resend] cpufreq: Support for fast frequency
 switching

On 03/25/2016 06:46 PM, Rafael J. Wysocki wrote:
>>> @@ -1726,6 +1810,34 @@ EXPORT_SYMBOL(cpufreq_unregister_notifie
>>> >>   *                              GOVERNORS                            *
>>> >>   *********************************************************************/
>>> >>
>>> >> +/**
>>> >> + * cpufreq_driver_fast_switch - Carry out a fast CPU frequency switch.
>>> >> + * @policy: cpufreq policy to switch the frequency for.
>>> >> + * @target_freq: New frequency to set (may be approximate).
>>> >> + *
>>> >> + * Carry out a fast frequency switch from interrupt context.
>> >
>> > I think that should say atomic rather than interrupt as this might not
>> > be called from interrupt context.
>
> "Interrupt context" here means something like "context that cannot
> sleep" and it's sort of a traditional way of calling that.  I
> considered saying "atomic context" here, but then decided that it
> might suggest too much.
> 
> Maybe something like "Carry out a fast frequency switch without
> sleeping" would be better?

Yes I do think that's preferable. I also wonder if it makes sense to
state expectations of how long the operation should take - i.e. not only
will it not sleep, but it is expected to complete "quickly." However I
accept that it is not well defined what that means. Maybe a mention that
this may be called in scheduler hot paths.