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Date: Fri, 12 Feb 2016 14:43:13 +0100
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Subject: Re: [PATCH 0/3] cpufreq: Replace timers with utilization update callbacks
From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Steve Muckle <steve.muckle@linaro.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM list <linux-pm@vger.kernel.org>,
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        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Juri Lelli <juri.lelli@arm.com>, Thomas Gleixner <tglx@linutronix.de>
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On Thu, Feb 11, 2016 at 8:04 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> On Thu, Feb 11, 2016 at 7:52 PM, Steve Muckle <steve.muckle@linaro.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