Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core

[Tom Lendacky]

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?