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)