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

From: Dietmar Eggemann
Date: Tue Jul 11 2017 - 11:21:13 EST

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
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.