linux-kernel - Re: [RFC V2 1/6] cpufreq: Replace "max_transition_latency" with "dynamic

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Message-ID: <20170714070142.GA14515@isilmar-4.linta.de>
Date:   Fri, 14 Jul 2017 09:01:42 +0200
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC V2 1/6] cpufreq: Replace "max_transition_latency" with
 "dynamic_switching"

On Thu, Jul 13, 2017 at 06:19:53PM +0200, Rafael J. Wysocki wrote:
> On Thu, Jul 13, 2017 at 7:40 AM, Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > There is no limitation in the ondemand or conservative governors which
> > disallow the transition_latency to be greater than 10 ms.
> >
> > The max_transition_latency field is rather used to disallow automatic
> > dynamic frequency switching for platforms which didn't wanted these
> > governors to run.
> >
> > Replace max_transition_latency with a boolean (dynamic_switching) and
> > check for transition_latency == CPUFREQ_ETERNAL along with that. This
> > makes it pretty straight forward to read/understand now.
> 
> Well, using CPUFREQ_ETERNAL for that on the driver side is still not
> particularly straightforward IMO, so maybe add a
> "no_dynamic_switching" to the driver structure and set it to "true"
> for the one driver in question?

IIRC it's not just one driver which sets the latency to CPUFREQ_ETERNAL, and
where dynamic switching might be harmful or at least lead to undefined
behavior.

Best,
	Dominik