Re: [PATCH v2 02/10] cpufreq: provide data for frequency-invariant load-tracking support

From: Sudeep Holla
Date: Thu Jul 13 2017 - 08:40:54 EST

On 11/07/17 16:21, Dietmar Eggemann wrote:
> On 11/07/17 07:39, Viresh Kumar wrote:
>> On 10-07-17, 14:46, Rafael J. Wysocki wrote:
>>> This particular change is about a new feature, so making it in the core is OK
>>> in two cases IMO: (a) when you actively want everyone to be affected by it and
>> IMO this change should be done for the whole ARM architecture. And if some
>> regression happens due to this, then we come back and solve it.
>>> (b) when the effect of it on the old systems should not be noticeable.
>> I am not sure about the effects of this on performance really.
>> @Dietmar: Any inputs for that ?
> Like I said in the other email, since for (future)
> arm/arm64 fast-switch driver, the return value of
> cpufreq_driver->fast_switch() does not give us the information that the
> frequency value did actually change, we have to implement

I was under the impression that we strictly don't care about that
information when I started exploring the fast_switch with the standard
firmware interface on ARM platforms(until if and when ARM provides an
instruction to achieve that).

If f/w failed to change the frequency, will that be not corrected in the
next sample or instance. I would like to know the impact of absence of
such notifications.

> arch_set_freq_scale() in the driver.
> This means that we probably only implement this in the subset of drivers
> which will be used in platforms on which we want to have
> frequency-invariant load-tracking.
> A future aperf/mperf like counter FIE solution can give us arch-wide
> support when those counters are available.