Messages in this thread | | | Date | Thu, 10 Dec 2020 18:04:39 +0530 | From | Viresh Kumar <> | Subject | Re: [PATCH] arm64: topology: Cleanup init_amu_fie() a bit |
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On 10-12-20, 11:29, Ionela Voinescu wrote: > On Thursday 10 Dec 2020 at 16:25:06 (+0530), Viresh Kumar wrote: > > - But right after that we call static_branch_disable() if we aren't > > invariant (call to topology_scale_freq_invariant()), and this will > > happen if amu_fie_cpus doesn't have all the CPUs there. Isn't it? So > > partial amu support is already disallowed, without cpufreq. > > > > This is the point that needs clarification: > > topology_scale_freq_invariant()) = cpufreq_supports_freq_invariance() || > arch_freq_counters_available(cpu_online_mask); > > This checks if the full system is invariant. > > The possible scenarios are: > > - All online CPUs support AMUs - arch_freq_counters_available() will > return true -> topology_scale_freq_invariant() will return true. > > - None of the CPUs support AMUs, or part of the CPUs support AMUs - the > system is invariant only if cpufreq is invariant (dependent on > whether the driver implements the proper callbacks that results in > calling arch_set_freq_scale() in cpufreq core. > > - Either cpufreq does not support invariance or we don't have AMU > support on all CPUs -> the system is not invariant so we disable > the AMU static key that guards the calls to > topology_scale_freq_tick() - we would not want to set a scale factor > for only a part of the CPUs. > > So whether were are or are not invariant does not depend only on the AMU > presence, but also on the cpufreq support for invariance. We have to > disable invariance altogether (including the AMU guarding static key) > if the system is not invariant (it no all CPUs have means to provide the > scale).
Okay, I think I mis-assumed that amu_fie_cpus will get set by enable_policy_freq_counters() even for CPUs where AMU support isn't there, it won't be though.
Having said that, this patch, along with the minor suggestion in the commit log, still stands fine, right ? The other patch which I sent is probably incorrect due to the above assumption I had.
-- viresh
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