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Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core
To:     Peter Zijlstra <peterz@infradead.org>,
        Giovanni Gherdovich <ggherdovich@suse.com>
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        Vincent Guittot <vincent.guittot@linaro.org>,
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        Valentin Schneider <valentin.schneider@arm.com>,
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        yazen.ghannam@amd.com, kim.phillips@amd.com,
        suravee.suthikulpanit@amd.com,
        "Fontenot, Nathan" <Nathan.Fontenot@amd.com>
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From:   Tom Lendacky <thomas.lendacky@amd.com>
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On 10/23/20 2:03 AM, Peter Zijlstra wrote:
> On Thu, Oct 22, 2020 at 10:10:35PM +0200, Giovanni Gherdovich wrote:
>> * for the AMD EPYC machines we haven't yet implemented frequency invariant
>>    accounting, which might explain why schedutil looses to ondemand on all
>>    the benchmarks.
> 
> Right, I poked the AMD people on that a few times, but nothing seems to
> be forthcoming :/ Tom, any way you could perhaps expedite the matter?

Adding Nathan to the thread to help out here.

Thanks,
Tom

> 
> In particular we're looking for some X86_VENDOR_AMD/HYGON code to run in
> 
>    arch/x86/kernel/smpboot.c:init_freq_invariance()
> 
> The main issue is finding a 'max' frequency that is not the absolute max
> turbo boost (this could result in not reaching it very often) but also
> not too low such that we're always clipping.
> 
> And while we're here, IIUC AMD is still using acpi_cpufreq, but AFAIK
> the chips have a CPPC interface which could be used instead. Is there
> any progress on that?
>