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

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Message-ID: <2395635.E95YnUO5Qt@vostro.rjw.lan>
Date:	Tue, 29 Mar 2016 14:10:45 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	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 Monday, March 28, 2016 09:47:53 AM Steve Muckle wrote:
> 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.

OK