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Date: Tue, 25 Aug 2020 13:20:57 +0530 From: Viresh Kumar <viresh.kumar@...aro.org> To: Ionela Voinescu <ionela.voinescu@....com> Cc: rjw@...ysocki.net, dietmar.eggemann@....com, catalin.marinas@....com, sudeep.holla@....com, will@...nel.org, valentin.schneider@....com, linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v3 5/5] arch_topology, arm, arm64: define arch_scale_freq_invariant() On 24-08-20, 22:02, Ionela Voinescu wrote: > From: Valentin Schneider <valentin.schneider@....com> > > arch_scale_freq_invariant() is used by schedutil to determine whether > the scheduler's load-tracking signals are frequency invariant. Its > definition is overridable, though by default it is hardcoded to 'true' > if arch_scale_freq_capacity() is defined ('false' otherwise). > > This behaviour is not overridden on arm, arm64 and other users of the > generic arch topology driver, which is somewhat precarious: > arch_scale_freq_capacity() will always be defined, yet not all cpufreq > drivers are guaranteed to drive the frequency invariance scale factor > setting. In other words, the load-tracking signals may very well *not* > be frequency invariant. > > Now that cpufreq can be queried on whether the current driver is driving > the Frequency Invariance (FI) scale setting, the current situation can > be improved. This combines the query of whether cpufreq supports the > setting of the frequency scale factor, with whether all online CPUs are > counter-based FI enabled. > > While cpufreq FI enablement applies at system level, for all CPUs, > counter-based FI support could also be used for only a subset of CPUs to > set the invariance scale factor. Therefore, if cpufreq-based FI support > is present, we consider the system to be invariant. If missing, we > require all online CPUs to be counter-based FI enabled in order for the > full system to be considered invariant. > > If the system ends up not being invariant, a new condition is needed in > the counter initialization code that disables all scale factor setting > based on counters. > > Precedence of counters over cpufreq use is not important here. The > invariant status is only given to the system if all CPUs have at least > one method of setting the frequency scale factor. > > Signed-off-by: Valentin Schneider <valentin.schneider@....com> > Signed-off-by: Ionela Voinescu <ionela.voinescu@....com> > Acked-by: Catalin Marinas <catalin.marinas@....com> > Cc: Catalin Marinas <catalin.marinas@....com> > Cc: Will Deacon <will@...nel.org> > Cc: Sudeep Holla <sudeep.holla@....com> > --- > arch/arm/include/asm/topology.h | 1 + > arch/arm64/include/asm/topology.h | 1 + > arch/arm64/kernel/topology.c | 7 +++++++ > drivers/base/arch_topology.c | 6 ++++++ > include/linux/arch_topology.h | 2 ++ > 5 files changed, 17 insertions(+) > > diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h > index e0593cf095d0..9219e67befbe 100644 > --- a/arch/arm/include/asm/topology.h > +++ b/arch/arm/include/asm/topology.h > @@ -9,6 +9,7 @@ > > /* Replace task scheduler's default frequency-invariant accounting */ > #define arch_scale_freq_capacity topology_get_freq_scale > +#define arch_scale_freq_invariant topology_scale_freq_invariant Maybe this macro should have been named arch_is_freq_invariant as all other ones are actually getting us a scaled number and this one is just a flag. But yeah, that is out of this series's scope, but maybe you should name topology_scale_freq_invariant() to topology_is_freq_invariant() or something else on those lines ? Anyway: Acked-by: Viresh Kumar <viresh.kumar@...aro.org> -- viresh
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