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SubjectRe: [PATCH] sched/fair: check for idle core


On Wed, 21 Oct 2020, Rafael J. Wysocki wrote:

> On Wednesday, October 21, 2020 2:42:20 PM CEST Julia Lawall wrote:
> >
> > On Wed, 21 Oct 2020, Peter Zijlstra wrote:
> >
> > > On Wed, Oct 21, 2020 at 01:56:55PM +0200, Julia Lawall wrote:
> > > > Prior to 5.8, my machine was using intel_pstate and had few background
> > > > tasks. Thus the problem wasn't visible in practice. Starting with 5.8
> > > > the kernel decided that intel_cpufreq would be more appropriate, which
> > > > introduced kworkers every 0.004 seconds on all cores.
> > >
> > > That still doesn't make any sense. Are you running the legacy on-demand
> > > thing or something?
> > >
> > > Rafael, Srinivas, Viresh, how come it defaults to that?
> >
> > The relevant commits are 33aa46f252c7, and 39a188b88332 that fixes a small
> > bug. I have a Intel(R) Xeon(R) CPU E7-8870 v4 @ 2.10GHz that does not
> > have the HWP feature, even though the cores seemed to be able to change
> > their frequencies at the hardware level.
>
> That's in the range of "turbo" P-states (if a P-state above a certain threshold
> is requested by the governor, the processor has a license to choose P-states
> in the range above this threshold by itself).

Sorry, but I don't understand this answer at all.

thanks,
julia

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