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Date: Mon, 11 Apr 2016 23:20:55 +0200
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Subject: Re: [PATCH 1/2] sched/fair: move cpufreq hook to update_cfs_rq_load_avg()
From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Steve Muckle <steve.muckle@linaro.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
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On Mon, Apr 11, 2016 at 9:28 PM, Steve Muckle <steve.muckle@linaro.org> wrote:
> Hi Rafael,
>
> On 04/01/2016 02:20 AM, Peter Zijlstra wrote:
>>> > My thinking was in CFS we get rid of the (cpu == smp_processor_id())
>>> > condition for calling the cpufreq hook.
>>> >
>>> > The sched governor can then calculate utilization and frequency required
>>> > for cpu. If (cpu == smp_processor_id()), the update is processed
>>> > normally. If (cpu != smp_processor_id()) and the new frequency is higher
>>> > than cpu's Fcur, the sched gov IPIs cpu to continue running the update
>>> > operation. Otherwise, the update is dropped.
>>> >
>>> > Does that sound plausible?
>>
>> Can be done I suppose..
>
> Currently we drop schedutil updates for a target CPU which do not occur
> on that CPU.
>
> Is this solely due to platforms which must run the cpufreq driver on the
> target CPU?

The current code assumes that the CPU running the update will always
be the one that gets updated.  Anything else would require extra
synchronization.

> Are there also shared cpufreq policies where the driver needs to run on
> any CPU in the affected policy/freq domain?

Yes, there are, AFAICS, but drivers are expected to cope with that (if
I understand the question correctly).

Thanks,
Rafael