[PATCH 2/3] x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC
From: Giovanni Gherdovich
Date: Tue Nov 10 2020 - 03:40:05 EST
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@xxxxxxx>
---
arch/x86/kernel/smpboot.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 89016cc96948..1e6fed437b0c 100644
--- 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;
--
2.26.2