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SubjectRe: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting
On 16/05/18 18:31, Juri Lelli wrote:
> On 16/05/18 17:47, Peter Zijlstra wrote:
> > On Wed, May 16, 2018 at 05:19:25PM +0200, Juri Lelli wrote:
> >
> > > Anyway, FWIW I started testing this on a E5-2609 v3 and I'm not seeing
> > > hackbench regressions so far (running with schedutil governor).
> >
> > https://en.wikipedia.org/wiki/Haswell_(microarchitecture)#Server_processors
> >
> > Lists the E5 2609 v3 as not having turbo at all, which is basically a
> > best case scenario for this patch.
> >
> > As I wrote earlier today; when turbo exists, like say the 2699, then
> > when we're busy we'll run at U=2.3/3.6 ~ .64, which might confuse
> > things.
>
> Indeed. I was mostly trying to see if adding this to the tick might
> introduce noticeable overhead.

Blindly testing on an i5-5200U (2.2/2.7 GHz) gave the following

# perf bench sched messaging --pipe --thread --group 2 --loop 20000

count mean std min 50% 95% 99% max
hostname kernel
i5-5200U test_after 30.0 13.843433 0.590605 12.369 13.810 14.85635 15.08205 15.127
test_before 30.0 13.571167 0.999798 12.228 13.302 15.57805 16.40029 16.690

It might be interesting to see what happens when using a single CPU
only?

Also, I will look at how the util signals look when a single CPU is
busy..

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