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

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Date:	Fri, 12 Feb 2016 14:43:13 +0100
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Steve Muckle <steve.muckle@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	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 8:04 PM, Rafael J. Wysocki <rafael@...nel.org> wrote:
> On Thu, Feb 11, 2016 at 7:52 PM, Steve Muckle <steve.muckle@...aro.org> wrote:
>> On 02/11/2016 09:30 AM, Peter Zijlstra wrote:
>>>> 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.
>>
>> But that's only true if the RT/DL tasks happen to be running when the
>> tick arrives right?
>>
>> Couldn't we have RT/DL activity which doesn't overlap with the tick? And
>> if no CFS tasks happen to be executing on that CPU, we'll never trigger
>> the cpufreq update. This could go on for an arbitrarily long time
>> depending on the periodicity of the work.
>
> I'm thinking that two additional hooks in enqueue_task_rt/dl() might
> help here.  Then, we will hit either the tick or enqueue and that
> should do the trick.
>
> Peter, what do you think?

In any case I posted a v9 with those changes
(https://patchwork.kernel.org/patch/8290791/).

Again, it doesn't appear to break things.

If the enqueue hooks are bad (unwanted at all or in wrong places),
please let me know.

Thanks,
Rafael