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x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC
authorGiovanni Gherdovich <ggherdovich@suse.cz>
Thu, 12 Nov 2020 18:26:13 +0000 (19:26 +0100)
committerIngo Molnar <mingo@kernel.org>
Fri, 11 Dec 2020 09:29:55 +0000 (10:29 +0100)
Frequency invariant accounting calculations need the ratio
freq_curr/freq_max, but freq_max is unknown as it depends on dynamic power
allocation between cores: AMD EPYC CPUs implement "Core Performance Boost".
Three candidates are considered to estimate this value:

- maximum non-boost frequency
- maximum boost frequency
- the mid point between the above two

Experimental data on an AMD EPYC Zen2 machine slightly favors the third
option, which is applied with this patch.

The analysis uses the ondemand cpufreq governor as baseline, and compares
it with schedutil in a number of configurations. Using the freq_max value
described above offers a moderate advantage in performance and efficiency:

sugov-max (freq_max=max_boost) performs the worst on tbench: less
throughput and reduced efficiency than the other invariant-schedutil
options (see "Data Overview" below). Consider that tbench is generally a
problematic case as no schedutil version currently is better than ondemand.

sugov-P0 (freq_max=max_P) is the worst on dbench, while the other sugov's
can surpass ondemand with less filesystem latency and slightly increased
efficiency.

1. DATA OVERVIEW
2. DETAILED PERFORMANCE TABLES
3. POWER CONSUMPTION TABLE

1. DATA OVERVIEW
================

sugov-noinv : non-invariant schedutil governor
sugov-max   : invariant schedutil, freq_max=max_boost
sugov-mid   : invariant schedutil, freq_max=midpoint
sugov-P0    : invariant schedutil, freq_max=max_P
perfgov     : performance governor

driver      : acpi_cpufreq
machine     : AMD EPYC 7742 (Zen2, aka "Rome"), dual socket,
              128 cores / 256 threads, SATA SSD storage, 250G of memory,
      XFS filesystem

Benchmarks are described in the next section.
Tilde (~) means the value is the same as baseline.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
            ondemand  perfgov  sugov-noinv  sugov-max  sugov-mid  sugov-P0  better if
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                                        PERFORMANCE RATIOS
tbench        1.00       1.44       0.90       0.87       0.93       0.93      higher
dbench        1.00       0.91       0.95       0.94       0.94       1.06      lower
kernbench     1.00       0.93       ~          ~          ~          0.97      lower
gitsource     1.00       0.66       0.97       0.96       ~          0.95      lower
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
                                    PERFORMANCE-PER-WATT RATIOS
tbench        1.00       1.16       0.84       0.84       0.88       0.85      higher
dbench        1.00       1.03       1.02       1.02       1.02       0.93      higher
kernbench     1.00       1.05       ~          ~          ~          ~         higher
gitsource     1.00       1.46       1.04       1.04       ~          1.05      higher

2. DETAILED PERFORMANCE TABLES
==============================

Benchmark          : tbench4 (i.e. dbench4 over the network, actually loopback)
Varying parameter  : number of clients
Unit               : MB/sec (higher is better)

                  5.9.0-ondemand (BASELINE)                   5.9.0-perfgov               5.9.0-sugov-noinv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Hmean  1        427.19  +- 0.16% (        )     778.35  +- 0.10% (  82.20%)     346.92  +- 0.14% ( -18.79%)
Hmean  2        853.82  +- 0.09% (        )    1536.23  +- 0.03% (  79.93%)     694.36  +- 0.05% ( -18.68%)
Hmean  4       1657.54  +- 0.12% (        )    2938.18  +- 0.12% (  77.26%)    1362.81  +- 0.11% ( -17.78%)
Hmean  8       3301.87  +- 0.06% (        )    5679.10  +- 0.04% (  72.00%)    2693.35  +- 0.04% ( -18.43%)
Hmean  16      6139.65  +- 0.05% (        )    9498.81  +- 0.04% (  54.71%)    4889.97  +- 0.17% ( -20.35%)
Hmean  32     11170.28  +- 0.09% (        )   17393.25  +- 0.08% (  55.71%)    9104.55  +- 0.09% ( -18.49%)
Hmean  64     19322.97  +- 0.17% (        )   31573.91  +- 0.08% (  63.40%)   18552.52  +- 0.40% (  -3.99%)
Hmean  128    30383.71  +- 0.11% (        )   37416.91  +- 0.15% (  23.15%)   25938.70  +- 0.41% ( -14.63%)
Hmean  256    31143.96  +- 0.41% (        )   30908.76  +- 0.88% (  -0.76%)   29754.32  +- 0.24% (  -4.46%)
Hmean  512    30858.49  +- 0.26% (        )   38524.60  +- 1.19% (  24.84%)   42080.39  +- 0.56% (  36.37%)
Hmean  1024   39187.37  +- 0.19% (        )   36213.86  +- 0.26% (  -7.59%)   39555.98  +- 0.12% (   0.94%)

                            5.9.0-sugov-max                 5.9.0-sugov-mid                  5.9.0-sugov-P0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Hmean  1        352.59  +- 1.03% ( -17.46%)     352.08  +- 0.75% ( -17.58%)     352.31  +- 1.48% ( -17.53%)
Hmean  2        697.32  +- 0.08% ( -18.33%)     700.16  +- 0.20% ( -18.00%)     696.79  +- 0.06% ( -18.39%)
Hmean  4       1369.88  +- 0.04% ( -17.35%)    1369.72  +- 0.07% ( -17.36%)    1365.91  +- 0.05% ( -17.59%)
Hmean  8       2696.79  +- 0.04% ( -18.33%)    2711.06  +- 0.04% ( -17.89%)    2715.10  +- 0.61% ( -17.77%)
Hmean  16      4725.03  +- 0.03% ( -23.04%)    4875.65  +- 0.02% ( -20.59%)    4953.05  +- 0.28% ( -19.33%)
Hmean  32      9231.65  +- 0.10% ( -17.36%)    8704.89  +- 0.27% ( -22.07%)   10562.02  +- 0.36% (  -5.45%)
Hmean  64     15364.27  +- 0.19% ( -20.49%)   17786.64  +- 0.15% (  -7.95%)   19665.40  +- 0.22% (   1.77%)
Hmean  128    42100.58  +- 0.13% (  38.56%)   34946.28  +- 0.13% (  15.02%)   38635.79  +- 0.06% (  27.16%)
Hmean  256    30660.23  +- 1.08% (  -1.55%)   32307.67  +- 0.54% (   3.74%)   31153.27  +- 0.12% (   0.03%)
Hmean  512    24604.32  +- 0.14% ( -20.27%)   40408.50  +- 1.10% (  30.95%)   38800.29  +- 1.23% (  25.74%)
Hmean  1024   35535.47  +- 0.28% (  -9.32%)   41070.38  +- 2.56% (   4.81%)   31308.29  +- 2.52% ( -20.11%)

Benchmark          : dbench (filesystem stressor)
Varying parameter  : number of clients
Unit               : seconds (lower is better)

NOTE-1: This dbench version measures the average latency of a set of filesystem
        operations, as we found the traditional dbench metric (throughput) to be
misleading.
NOTE-2: Due to high variability, we partition the original dataset and apply
        statistical bootrapping (a resampling method). Accuracy is reported in the
form of 95% confidence intervals.

                  5.9.0-ondemand (BASELINE)                   5.9.0-perfgov               5.9.0-sugov-noinv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
SubAmean  1         98.79  +- 0.92 (        )      83.36  +- 0.82 (  15.62%)      84.82  +- 0.92 (  14.14%)
SubAmean  2        116.00  +- 0.89 (        )     102.12  +- 0.77 (  11.96%)     109.63  +- 0.89 (   5.49%)
SubAmean  4        149.90  +- 1.03 (        )     132.12  +- 0.91 (  11.86%)     143.90  +- 1.15 (   4.00%)
SubAmean  8        182.41  +- 1.13 (        )     159.86  +- 0.93 (  12.36%)     165.82  +- 1.03 (   9.10%)
SubAmean  16       237.83  +- 1.23 (        )     219.46  +- 1.14 (   7.72%)     229.28  +- 1.19 (   3.59%)
SubAmean  32       334.34  +- 1.49 (        )     309.94  +- 1.42 (   7.30%)     321.19  +- 1.36 (   3.93%)
SubAmean  64       576.61  +- 2.16 (        )     540.75  +- 2.00 (   6.22%)     551.27  +- 1.99 (   4.39%)
SubAmean  128     1350.07  +- 4.14 (        )    1205.47  +- 3.20 (  10.71%)    1280.26  +- 3.75 (   5.17%)
SubAmean  256     3444.42  +- 7.97 (        )    3698.00 +- 27.43 (  -7.36%)    3494.14  +- 7.81 (  -1.44%)
SubAmean  2048   39457.89 +- 29.01 (        )   34105.33 +- 41.85 (  13.57%)   39688.52 +- 36.26 (  -0.58%)

                            5.9.0-sugov-max                 5.9.0-sugov-mid                  5.9.0-sugov-P0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
SubAmean  1         85.68  +- 1.04 (  13.27%)      84.16  +- 0.84 (  14.81%)      83.99  +- 0.90 (  14.99%)
SubAmean  2        108.42  +- 0.95 (   6.54%)     109.91  +- 1.39 (   5.24%)     112.06  +- 0.91 (   3.39%)
SubAmean  4        136.90  +- 1.04 (   8.67%)     137.59  +- 0.93 (   8.21%)     136.55  +- 0.95 (   8.91%)
SubAmean  8        163.15  +- 0.96 (  10.56%)     166.07  +- 1.02 (   8.96%)     165.81  +- 0.99 (   9.10%)
SubAmean  16       224.86  +- 1.12 (   5.45%)     223.83  +- 1.06 (   5.89%)     230.66  +- 1.19 (   3.01%)
SubAmean  32       320.51  +- 1.38 (   4.13%)     322.85  +- 1.49 (   3.44%)     321.96  +- 1.46 (   3.70%)
SubAmean  64       553.25  +- 1.93 (   4.05%)     554.19  +- 2.08 (   3.89%)     562.26  +- 2.22 (   2.49%)
SubAmean  128     1264.35  +- 3.72 (   6.35%)    1256.99  +- 3.46 (   6.89%)    2018.97 +- 18.79 ( -49.55%)
SubAmean  256     3466.25  +- 8.25 (  -0.63%)    3450.58  +- 8.44 (  -0.18%)    5032.12 +- 38.74 ( -46.09%)
SubAmean  2048   39133.10 +- 45.71 (   0.82%)   39905.95 +- 34.33 (  -1.14%)   53811.86 +-193.04 ( -36.38%)

Benchmark          : kernbench (kernel compilation)
Varying parameter  : number of jobs
Unit               : seconds (lower is better)

                  5.9.0-ondemand (BASELINE)                   5.9.0-perfgov               5.9.0-sugov-noinv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Amean  2        471.71 +- 26.61% (        )     409.88 +- 16.99% (  13.11%)     430.63  +- 0.18% (   8.71%)
Amean  4        211.87  +- 0.58% (        )     194.03  +- 0.74% (   8.42%)     215.33  +- 0.64% (  -1.63%)
Amean  8        109.79  +- 1.27% (        )     101.43  +- 1.53% (   7.61%)     111.05  +- 1.95% (  -1.15%)
Amean  16        59.50  +- 1.28% (        )      55.61  +- 1.35% (   6.55%)      59.65  +- 1.78% (  -0.24%)
Amean  32        34.94  +- 1.22% (        )      32.36  +- 1.95% (   7.41%)      35.44  +- 0.63% (  -1.43%)
Amean  64        22.58  +- 0.38% (        )      20.97  +- 1.28% (   7.11%)      22.41  +- 1.73% (   0.74%)
Amean  128       17.72  +- 0.44% (        )      16.68  +- 0.32% (   5.88%)      17.65  +- 0.96% (   0.37%)
Amean  256       16.44  +- 0.53% (        )      15.76  +- 0.32% (   4.18%)      16.76  +- 0.60% (  -1.93%)
Amean  512       16.54  +- 0.21% (        )      15.62  +- 0.41% (   5.53%)      16.84  +- 0.85% (  -1.83%)

                            5.9.0-sugov-max                 5.9.0-sugov-mid                  5.9.0-sugov-P0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Amean  2        421.30  +- 0.24% (  10.69%)     419.26  +- 0.15% (  11.12%)     414.38  +- 0.33% (  12.15%)
Amean  4   217.81  +- 5.53% (  -2.80%)     211.63  +- 0.99% (   0.12%)     208.43  +- 0.47% (   1.63%)
Amean  8   108.80  +- 0.43% (   0.90%)     108.48  +- 1.44% (   1.19%)     108.59  +- 3.08% (   1.09%)
Amean  16   58.84  +- 0.74% (   1.12%)      58.37  +- 0.94% (   1.91%)      57.78  +- 0.78% (   2.90%)
Amean  32   34.04  +- 2.00% (   2.59%)      34.28  +- 1.18% (   1.91%)      33.98  +- 2.21% (   2.75%)
Amean  64   22.22  +- 1.69% (   1.60%)      22.27  +- 1.60% (   1.38%)      22.25  +- 1.41% (   1.47%)
Amean  128  17.55  +- 0.24% (   0.97%)      17.53  +- 0.94% (   1.04%)      17.49  +- 0.43% (   1.30%)
Amean  256  16.51  +- 0.46% (  -0.40%)      16.48  +- 0.48% (  -0.19%)      16.44  +- 1.21% (   0.00%)
Amean  512  16.50  +- 0.35% (   0.19%)      16.35  +- 0.42% (   1.14%)      16.37  +- 0.33% (   0.99%)

Benchmark          : gitsource (time to run the git unit test suite)
Varying parameter  : none
Unit               : seconds (lower is better)

                  5.9.0-ondemand (BASELINE)                   5.9.0-perfgov               5.9.0-sugov-noinv
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Amean          1035.76  +- 0.30% (        )     688.21  +- 0.04% (  33.56%)    1003.85  +- 0.14% (   3.08%)

                            5.9.0-sugov-max                 5.9.0-sugov-mid                  5.9.0-sugov-P0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Amean           995.82  +- 0.08% (   3.86%)    1011.98  +- 0.03% (   2.30%)     986.87  +- 0.19% (   4.72%)

3. POWER CONSUMPTION TABLE
==========================

Average power consumption (watts).

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
            ondemand  perfgov  sugov-noinv  sugov-max  sugov-mid  sugov-P0
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
tbench4     227.25     281.83     244.17     236.76     241.50     247.99
dbench4     151.97     161.87     157.08     158.10     158.06     153.73
kernbench   162.78     167.22     162.90     164.19     164.65     164.72
gitsource   133.65     139.00     133.04     134.43     134.18     134.32

Signed-off-by: Giovanni Gherdovich <ggherdovich@suse.cz>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20201112182614.10700-3-ggherdovich@suse.cz
arch/x86/kernel/smpboot.c patch | blob | history

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index a4ab5cf..c5dd5f6 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -2054,6 +2054,8 @@ static bool amd_set_max_freq_ratio(void)
        }
 
        perf_ratio = div_u64(highest_perf * SCHED_CAPACITY_SCALE, nominal_perf);
+       /* midpoint between max_boost and max_P */
+       perf_ratio = (perf_ratio + SCHED_CAPACITY_SCALE) >> 1;
        if (!perf_ratio) {
                pr_debug("Non-zero highest/nominal perf values led to a 0 ratio\n");
                return false;
Domain: System / Kernel;