Messages in this thread | | | Date | Wed, 2 Sep 2020 14:24:28 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH v5 5/5] arch_topology, arm, arm64: define arch_scale_freq_invariant() |
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On Tue, Sep 01, 2020 at 09:55:49PM +0100, Ionela Voinescu wrote: > From: Valentin Schneider <valentin.schneider@arm.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@arm.com> > Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> > Acked-by: Catalin Marinas <catalin.marinas@arm.com> > Acked-by: Viresh Kumar <viresh.kumar@linaro.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
-- Regards, Sudeep
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