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SubjectRe: [PATCH v3 1/1] x86,sched: On AMD EPYC set freq_max = max_boost in schedutil invariant formula
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On Wed, 2021-02-03 at 19:25 +0100, Rafael J. Wysocki wrote:
> [cut]
>
> So below is a prototype of an alternative fix for the issue at hand.
>
> I can't really test it here, because there's no _CPC in the ACPI tables of my
> test machines, so testing it would be appreciated. However, AFAICS these
> machines are affected by the performance issue related to the scale-invariance
> when they are running acpi-cpufreq, so what we are doing here is not entirely
> sufficient.
>
> It looks like the scale-invariance code should ask the cpufreq driver about
> the maximum frequency and note that cpufreq drivers may be changed on the
> fly.
>
> What the patch below does is to add an extra entry to the frequency table for
> each CPU to represent the maximum "boost" frequency, so as to cause that
> frequency to be used as cpuinfo.max_freq.
>
> The reason why I think it is better to extend the frequency tables instead
> of simply increasing the frequency for the "P0" entry is because the latter
> may cause "turbo" frequency to be asked for less often.
>
> ---
> drivers/cpufreq/acpi-cpufreq.c | 107 ++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 95 insertions(+), 12 deletions(-)

Hello Rafael,

thanks for looking at this. Your patch is indeed cleaner than the one I proposed.

Preliminary testing is favorable; more tests are running.

Results from your patch are in the fourth column below; the performance from
v5.10 looks restored.

I'll follow up once the tests I queued are completed.

Giovanni


TEST : Intel Open Image Denoise, www.openimagedenoise.org
INVOCATION : ./denoise -hdr memorial.pfm -out out.pfm -bench 200 -threads $NTHREADS
CPU : MODEL : 2x AMD EPYC 7742
FREQUENCY TABLE : P2: 1.50 GHz
P1: 2.00 GHz
P0: 2.25 GHz
MAX BOOST : 3.40 GHz

Results: threads, msecs (ratio). Lower is better.

v5.10 v5.11-rc4 v5.11-rc4-ggherdov v5.11-rc6-rafael
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 1069.85 (1.00) 1071.84 (1.00) 1070.42 (1.00) 1069.12 (1.00)
2 542.24 (1.00) 544.40 (1.00) 544.48 (1.00) 540.81 (1.00)
4 278.00 (1.00) 278.44 (1.00) 277.72 (1.00) 277.79 (1.00)
8 149.81 (1.00) 149.61 (1.00) 149.87 (1.00) 149.51 (1.00)
16 79.01 (1.00) 79.31 (1.00) 78.94 (1.00) 79.02 (1.00)
24 58.01 (1.00) 58.51 (1.01) 58.15 (1.00) 57.84 (1.00)
32 46.58 (1.00) 48.30 (1.04) 46.66 (1.00) 46.70 (1.00)
48 37.29 (1.00) 51.29 (1.38) 37.27 (1.00) 38.10 (1.02)
64 34.01 (1.00) 49.59 (1.46) 33.71 (0.99) 34.51 (1.01)
80 31.09 (1.00) 44.27 (1.42) 31.33 (1.01) 31.11 (1.00)
96 28.56 (1.00) 40.82 (1.43) 28.47 (1.00) 28.65 (1.00)
112 28.09 (1.00) 40.06 (1.43) 28.63 (1.02) 28.38 (1.01)
120 28.73 (1.00) 39.78 (1.38) 28.14 (0.98) 28.16 (0.98)
128 28.93 (1.00) 39.60 (1.37) 29.38 (1.02) 28.55 (0.99)

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