Hi, On Thursday 02 Jul 2020 at 08:28:18 (+0530), Viresh Kumar wrote: > On 01-07-20, 18:05, Rafael J. Wysocki wrote: > > On Wed, Jul 1, 2020 at 3:33 PM Ionela Voinescu <ionela.voine...@arm.com> > > wrote: > > > On Wednesday 01 Jul 2020 at 16:16:17 (+0530), Viresh Kumar wrote: > > > > I will rather suggest CPUFREQ_SKIP_SET_FREQ_SCALE as the name and > > > > functionality. We need to give drivers a choice if they do not want > > > > the core to do it on their behalf, because they are doing it on their > > > > own or they don't want to do it. > > > > Well, this would go backwards to me, as we seem to be designing an > > opt-out flag for something that's not even implemented already. > > > > I would go for an opt-in instead. That would be much cleaner and less > > prone to regressions IMO. > > That's fine, I just wanted an option for drivers to opt-out of this > thing. I felt okay with the opt-out flag as this should be enabled for > most of the drivers and so enabling by default looked okay as well. > > > > In this case we would not be able to tell if cpufreq (driver or core) > > > can provide the frequency scale factor, so we would not be able to tell > > > if the system is really frequency invariant; CPUFREQ_SKIP_SET_FREQ_SCALE > > That is easy to fix. Let the drivers call > enable_cpufreq_freq_invariance() and set the flag. >
Right! I suppose part of "the dream" :) was for drivers to be ignorant of frequency invariance, and for the core to figure out if it has proper information to potentially* pass to the scheduler. *potentially = depending on the arch_set_freq_scale() definition. > > > would be set if either: > > > - the driver calls arch_set_freq_scale() on its own > > > - the driver does not want arch_set_freq_scale() to be called. > > > > > > So at the core level we would not be able to distinguish between the > > > two, and return whether cpufreq-based invariance is supported. > > > > > > I don't really see a reason why a driver would not want to set the > > > frequency scale factor > > A simple case where the driver doesn't have any idea what the real > freq For me, this would have been filtered by either the type of callback they use (target_index(), fast_switch() and even target() would offer some close to accurate indication of the current frequency, while setpolicy() it obviously targets a range of frequencies) or by the definition of arch_set_freq_scale(). > ..of the CPU is and it doesn't have counters to guess it as well. > > There can be other reasons which we aren't able to imagine at this > point of time. > But I understand both the points you and Rafael raised so it's obvious that a 'opt in' flag would be the better option. Thank you both, Ionela. > -- > viresh
