linux-kernel - Re: [PATCH 0/3] cpufreq: Replace timers with utilization update callbacks

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Message-ID: <20160211173033.GP6357@twins.programming.kicks-ass.net>
Date:	Thu, 11 Feb 2016 18:30:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steve Muckle <steve.muckle@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Linux PM list <linux-pm@...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>,
	Juri Lelli <juri.lelli@....com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/3] cpufreq: Replace timers with utilization update
 callbacks

On Thu, Feb 11, 2016 at 09:06:04AM -0800, Steve Muckle wrote:
> Hi Peter,
> 
> >> > I think additional hooks such as enqueue/dequeue would be needed in
> >> > RT/DL.

That is what I reacted to mostly. Enqueue/dequeue hooks don't really
make much sense for RT / DL.

> Rafael's changes aren't specifying particular frequencies/capacities in
> the scheduler hooks. They're just pokes to get cpufreq to run, in order
> to eliminate cpufreq's timers.
> 
> My concern above is that pokes are guaranteed to keep occurring when
> there is only RT or DL activity so nothing breaks.

The hook in their respective tick handler should ensure stuff is called
sporadically and isn't stalled.