Re: [tip: sched/core] sched/eevdf: Curb wakeup-preemption

From: K Prateek Nayak
Date: Fri Aug 25 2023 - 02:42:52 EST

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Hello again,

On 8/22/2023 11:39 AM, Mike Galbraith wrote:
> Methinks these shards are due to tbench simply being one of those
> things that happens to like the CFS notion of short term fairness a bit
> better than the EEVDF notion, ie are inevitable fallout tied to the
> very thing that makes EEVDF service less spiky that CFS, and thus will
> be difficult to sweep up.

Ah! That is pretty sad for some of these benchmarks that are not a
fan of large number of context-switches. I went back and tried some
solutions floating in the community (thank you Mathieu and Aaron)

>
> Too bad I didn't save Peter's test hack to make EEVDF use the same
> notion of fair (not a keeper) as I think that would likely prove it.

More benchmarking with Mathieu's [1] and Aaron's [2] proposed changes
on top of EEVDF + Curb Wakeup-Preemption:

tl;dr

- Hackbench is now happy with Mathieu's and Aaron's patches (I'm not
looking with CFS baseline for now since Swapnil and Gautham are
testing those)

- Some unixbench variants are pretty happy in overloaded system.

- schbench is pretty happy throughout.

- tbench and DeathStarBench are still pretty unhappy. Most likely
because of greater number of context switches but I'll get more
concrete evidence for this.

- Other micro-benchmarks tested are more or less perf neutral to EEVDF.

o System Details

- 3rd Generation EPYC System
- 2 x 64C/128T
- NPS1 mode

o Kernels

base (updated): tip:sched/core at commit 88c56cfeaec4 ("sched/fair: Block nohz tick_stop when cfs bandwidth in use")
eevdf: tip:sched/core at commit c1fc6484e1fb ("sched/rt: sysctl_sched_rr_timeslice show default timeslice after reset")
eevdf_curb: tip:sched/core at commit 63304558ba5d ("sched/eevdf:Curb wakeup-preemption")
eevdf-curb+mathieu: eevdf + cheery-pick commit e242aa146918 ("sched/eevdf: Curb wakeup-preemption") + Mathieu's patches [1]
eevdf-curb+mathieu+aaron eevdf-curb+mathieu + Aaron's patch [2]

[References]

[1] "sched: Skip queued wakeups only when L2 is shared"
(https://lore.kernel.org/all/20230822113133.643238-1-mathieu.desnoyers@xxxxxxxxxxxx/)
[2] "Reduce cost of accessing tg->load_avg"
(https://lore.kernel.org/lkml/20230823060832.454842-1-aaron.lu@xxxxxxxxx/)

o Benchmark Results

* - Interesting Regression
^ - Interesting Improvement

==================================================================
Test : hackbench
Units : Normalized time in seconds
Interpretation: Lower is better
Statistic : AMean
==================================================================
Case: base[pct imp](CV) eevdf[pct imp](CV) eevdf-curb[pct imp](CV) eevdf-curb+mathieu[pct imp](CV) eevdf-curb+mathieu+aaron[pct imp](CV)
1-groups 1.00 [ -0.00]( 2.64) 1.02 [ -1.98]( 1.89) 1.03 [ -2.83]( 2.42) 0.95 [ 5.10]( 2.65) 0.94 [ 5.67]( 2.07) ^
2-groups 1.00 [ -0.00]( 2.97) 1.05 [ -5.18]( 2.04) 1.04 [ -4.24]( 1.25) 0.98 [ 1.88]( 1.99) 0.96 [ 3.76]( 2.64) ^
4-groups 1.00 [ -0.00]( 1.84) 1.06 [ -6.07]( 2.38) 1.05 [ -5.42]( 1.68) 1.00 [ 0.43]( 1.50) 0.99 [ 0.65]( 0.97)
8-groups 1.00 [ -0.00]( 1.24) 1.07 [ -7.09]( 1.52) 1.07 [ -7.29]( 1.32) 0.91 [ 9.11]( 1.63) 0.93 [ 7.49]( 2.43) ^
16-groups 1.00 [ -0.00]( 3.31) 1.05 [ -4.98]( 3.44) 1.05 [ -5.27]( 2.58) 0.74 [ 26.35]( 1.22) 0.69 [ 31.04]( 1.90) ^

==================================================================
Test : tbench
Units : Normalized throughput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: base[pct imp](CV) eevdf[pct imp](CV) eevdf-curb[pct imp](CV) eevdf-curb+mathieu[pct imp](CV) eevdf-curb+mathieu+aaron[pct imp](CV)
1 1.00 [ 0.00]( 1.08) 1.00 [ 0.42]( 0.18) 1.00 [ -0.03]( 0.06) 0.99 [ -0.57]( 0.27) 0.99 [ -0.51]( 0.97)
2 1.00 [ 0.00]( 0.69) 1.00 [ -0.09]( 0.63) 0.99 [ -0.81]( 0.63) 1.00 [ -0.15]( 0.74) 0.99 [ -0.76]( 0.76)
4 1.00 [ 0.00]( 0.70) 0.99 [ -1.20]( 0.86) 1.00 [ -0.26]( 1.19) 0.99 [ -1.08]( 1.03) 0.99 [ -1.43]( 0.84)
8 1.00 [ 0.00]( 0.85) 1.01 [ 0.56]( 0.22) 1.00 [ 0.35]( 0.73) 1.00 [ -0.32]( 0.53) 1.00 [ -0.22]( 1.45)
16 1.00 [ 0.00]( 2.18) 0.98 [ -1.82]( 1.99) 0.99 [ -0.92]( 1.36) 0.99 [ -1.19]( 1.54) 0.97 [ -3.33]( 1.44)
32 1.00 [ 0.00]( 3.84) 0.99 [ -0.88]( 4.29) 1.00 [ 0.06]( 2.21) 0.98 [ -1.92]( 3.60) 0.96 [ -4.36]( 2.45)
64 1.00 [ 0.00]( 7.06) 1.03 [ 3.45]( 1.71) 1.02 [ 1.68]( 3.06) 1.03 [ 2.60]( 3.37) 1.01 [ 0.57]( 3.97)
128 1.00 [ 0.00]( 0.88) 1.02 [ 1.54]( 0.65) 0.98 [ -1.74]( 0.62) 0.98 [ -1.63]( 1.85) 0.97 [ -3.33]( 1.83)
256 1.00 [ 0.00]( 0.88) 0.94 [ -5.67]( 0.19) 0.92 [ -8.10]( 0.50) 0.95 [ -4.94]( 0.21) 0.91 [ -8.74]( 1.55) *
512 1.00 [ 0.00]( 0.07) 0.91 [ -9.17]( 0.20) 0.90 [-10.39]( 0.29) 0.92 [ -8.37]( 1.51) 0.90 [ -9.73]( 0.05) *
1024 1.00 [ 0.00]( 0.30) 0.87 [-12.66]( 0.29) 0.86 [-13.64]( 0.49) 0.86 [-14.47]( 0.35) 0.87 [-13.44]( 0.26) *

==================================================================
Test : stream-10
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: base[pct imp](CV) eevdf[pct imp](CV) eevdf-curb[pct imp](CV) eevdf-curb+mathieu[pct imp](CV) eevdf-curb+mathieu+aaron[pct imp](CV)
Copy 1.00 [ 0.00]( 8.87) 1.03 [ 2.94]( 4.32) 1.05 [ 5.23]( 2.73) 0.96 [ -3.92]( 7.61) 0.97 [ -3.28]( 5.93)
Scale 1.00 [ 0.00]( 6.80) 1.01 [ 1.38]( 5.21) 1.01 [ 1.03]( 5.48) 1.03 [ 2.98]( 1.04) 0.99 [ -1.24]( 7.22)
Add 1.00 [ 0.00]( 7.24) 1.01 [ 1.45]( 6.25) 1.01 [ 1.39]( 5.53) 1.02 [ 1.51]( 2.51) 0.98 [ -2.02]( 6.99)
Triad 1.00 [ 0.00]( 5.00) 0.96 [ -3.63](10.74) 1.00 [ 0.18]( 7.14) 0.99 [ -0.78]( 5.21) 1.00 [ 0.45]( 2.91)

==================================================================
Test : stream-100
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: base[pct imp](CV) eevdf[pct imp](CV) eevdf-curb[pct imp](CV) eevdf-curb+mathieu[pct imp](CV) eevdf-curb+mathieu+aaron[pct imp](CV)
Copy 1.00 [ 0.00]( 0.45) 1.00 [ -0.27]( 0.70) 1.00 [ -0.27]( 1.08) 1.00 [ -0.48]( 1.44) 0.98 [ -2.02]( 4.84)
Scale 1.00 [ 0.00]( 4.40) 0.98 [ -1.86]( 6.55) 1.01 [ 1.25]( 0.82) 0.99 [ -0.85]( 4.98) 1.01 [ 1.10]( 1.07)
Add 1.00 [ 0.00]( 4.97) 0.99 [ -0.91]( 6.53) 1.02 [ 2.20]( 1.08) 1.00 [ 0.26]( 4.90) 1.00 [ 0.11]( 2.37)
Triad 1.00 [ 0.00]( 0.24) 0.95 [ -4.85]( 6.66) 0.98 [ -2.19]( 4.56) 0.97 [ -2.80]( 5.56) 0.98 [ -1.58]( 2.15)

==================================================================
Test : netperf
Units : Normalized Througput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: base[pct imp](CV) eevdf[pct imp](CV) eevdf-curb[pct imp](CV) eevdf-curb+mathieu[pct imp](CV) eevdf-curb+mathieu+aaron[pct imp](CV)
1-clients 1.00 [ 0.00]( 0.46) 0.99 [ -1.26]( 0.46) 0.99 [ -0.67]( 0.70) 1.00 [ -0.13]( 0.30) 0.99 [ -1.46]( 0.37)
2-clients 1.00 [ 0.00]( 0.75) 0.99 [ -0.87]( 0.38) 1.00 [ -0.21]( 0.92) 1.00 [ 0.13]( 0.32) 0.99 [ -1.47]( 1.05)
4-clients 1.00 [ 0.00]( 0.84) 1.00 [ -0.45]( 0.72) 1.00 [ -0.14]( 0.83) 1.00 [ -0.10]( 0.60) 0.99 [ -0.70]( 0.78)
8-clients 1.00 [ 0.00]( 0.78) 0.99 [ -1.07]( 0.98) 0.99 [ -0.63]( 0.82) 1.00 [ -0.49]( 0.85) 0.99 [ -0.83]( 0.81)
16-clients 1.00 [ 0.00]( 2.56) 1.00 [ -0.29]( 0.70) 1.00 [ 0.03]( 1.26) 1.00 [ 0.17]( 0.66) 1.00 [ -0.43]( 0.80)
32-clients 1.00 [ 0.00]( 1.03) 0.99 [ -0.76]( 0.74) 0.99 [ -0.73]( 1.24) 1.00 [ -0.49]( 1.45) 0.99 [ -1.29]( 1.88)
64-clients 1.00 [ 0.00]( 2.69) 0.98 [ -1.96]( 2.24) 0.99 [ -1.39]( 3.06) 0.98 [ -1.78]( 3.00) 0.98 [ -2.31]( 3.00)
128-clients 1.00 [ 0.00]( 1.91) 1.00 [ -0.43]( 1.72) 0.99 [ -0.64]( 1.64) 0.97 [ -2.72]( 1.34) 1.00 [ -0.49]( 1.83)
256-clients 1.00 [ 0.00]( 2.21) 1.02 [ 2.23]( 4.44) 1.00 [ 0.29]( 3.71) 1.01 [ 1.49]( 3.72) 1.02 [ 2.17]( 2.50)
512-clients 1.00 [ 0.00](45.18) 1.00 [ 0.10](52.42) 0.97 [ -2.76](57.69) 0.99 [ -1.14](49.76) 0.99 [ -0.58](50.33)

==================================================================
Test : schbench (old)
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: base[pct imp](CV) eevdf[pct imp](CV) eevdf-curb[pct imp](CV) eevdf-curb+mathieu[pct imp](CV) eevdf-curb+mathieu+aaron[pct imp](CV)
1 1.00 [ -0.00](12.03) 1.09 [ -8.70]( 2.28) 1.09 [ -8.70]( 2.28) 0.96 [ 4.35](17.83) 1.13 [-13.04]( 5.95)
2 1.00 [ -0.00]( 9.36) 1.08 [ -7.69]( 6.42) 0.96 [ 3.85](11.02) 1.00 [ -0.00]( 2.19) 0.92 [ 7.69]( 0.00)
4 1.00 [ -0.00]( 1.95) 1.00 [ -0.00]( 3.77) 0.93 [ 6.67]( 4.22) 1.03 [ -3.33]( 3.81) 0.93 [ 6.67]( 5.52)
8 1.00 [ -0.00]( 9.01) 1.03 [ -2.70](13.83) 0.95 [ 5.41]( 1.63) 1.08 [ -8.11]( 2.94) 1.05 [ -5.41]( 3.01)
16 1.00 [ -0.00]( 3.08) 0.94 [ 6.00]( 4.37) 1.00 [ -0.00]( 3.53) 1.06 [ -6.00]( 1.10) 0.98 [ 2.00]( 5.51)
32 1.00 [ -0.00]( 0.75) 1.05 [ -5.19]( 8.69) 1.01 [ -1.30]( 5.14) 1.01 [ -1.30]( 5.14) 0.95 [ 5.19]( 5.36)
64 1.00 [ -0.00]( 2.15) 0.96 [ 4.29]( 2.30) 0.98 [ 1.84]( 2.56) 0.93 [ 7.36](14.38) 0.90 [ 9.82](15.50)
128 1.00 [ -0.00]( 5.18) 1.01 [ -0.57](12.12) 1.14 [-14.29]( 6.76) 1.09 [ -9.43]( 8.88) 1.04 [ -4.29]( 4.46)
256 1.00 [ -0.00]( 4.18) 0.16 [ 83.86](26.04) 0.18 [ 82.36]( 8.04) 0.16 [ 83.69](21.07) 0.19 [ 81.29]( 2.30) ^
512 1.00 [ -0.00]( 2.10) 0.29 [ 70.52]( 5.62) 0.29 [ 70.80]( 3.48) 0.30 [ 70.45]( 1.73) 0.30 [ 70.17]( 5.31) ^

==================================================================
Test : Unixbench
Units : Various, Throughput
Interpretation: Higher is better
Statistic : AMean, Hmean (Specified)
==================================================================
base eevdf eevdf_curb eevdf-curb+mathieu eevdf-curb+mathieu+aaron
Hmean unixbench-dhry2reg-1 41407024.82 ( 0.00%) 41248390.97 ( -0.38%) 41576959.80 ( 0.41%) 41641988.85 ( 0.57%) 40989184.46 ( -1.01%)
Hmean unixbench-dhry2reg-512 6249629291.88 ( 0.00%) 6239969914.15 ( -0.15%) 6223263669.12 ( -0.42%) 6258072789.83 ( 0.14%) 6243186854.90 ( -0.10%)
Amean unixbench-syscall-1 2922580.63 ( 0.00%) 2968518.27 * -1.57%* 2923093.63 ( -0.02%) 2887947.73 * 1.19%* 2921456.17 ( 0.04%)
Amean unixbench-syscall-512 7606400.73 ( 0.00%) 7790656.20 * 2.42%* 8300980.77 * 9.13%* 7743306.30 * 1.80%* 8284260.83 * 8.91%* ^
Hmean unixbench-pipe-1 2574942.54 ( 0.00%) 2535689.01 * -1.52%* 2472718.52 * -3.97%* 2558661.32 * -0.63%* 2567755.92 * -0.28%*
Hmean unixbench-pipe-512 364489246.31 ( 0.00%) 361385055.25 * -0.85%* 363215893.62 * -0.35%* 368809317.33 * 1.19%* 370896020.69 * 1.76%*
Hmean unixbench-spawn-1 4428.94 ( 0.00%) 4506.26 ( 1.75%) 4520.53 ( 2.07%) 4778.12 * 7.88%* 4353.00 ( -1.71%)
Hmean unixbench-spawn-512 68883.47 ( 0.00%) 69380.09 ( 0.72%) 69709.04 * 1.20%* 70278.77 * 2.03%* 71187.47 * 3.34%*
Hmean unixbench-execl-1 3878.47 ( 0.00%) 3824.57 * -1.39%* 3835.20 * -1.12%* 3802.46 * -1.96%* 3830.36 * -1.24%*
Hmean unixbench-execl-512 11638.84 ( 0.00%) 12288.64 ( 5.58%) 13096.25 * 12.52%* 12976.96 * 11.50%* 12468.95 ( 7.13%) ^

==================================================================
Test : ycsb-mongodb
Units : Throughput
Interpretation: Higher is better
Statistic : AMean
==================================================================

tip: 301757.33 (var: 1.63%) (%diff: +0.00%)
eevdf: 309589.33 (var: 1.41%) (%diff: +2.60%)
eevdf_curb; 303940.00 (var: 1.09%) (%diff: +0.72%)
eevdf-curb+mathieu: 303055.67 (var: 4.14%) (%diff: +0.43%)
eevdf-curb+mathieu+aaron: 297810.00 (var: 0.45%) (%diff: -1.31%)

==================================================================
Test : DeathStarBench
Units : %diff of Throughput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Scaling base eevdf eevdf_curb eevdf-curb+mathieu eevdf-curb+mathieu+aaron
1CCD 0% -14.95% -16.35% -16.67% -16.22% *
2CCD 0% -13.50% -15.94% -18.03% -17.93% *
4CCD 0% -8.49% -11.07% -13.11% -14.57% *
8CCD 0% -4.61% -4.87% -5.72% -6.02% *

--

I'll go back and dig further.

--
Thanks and Regards,
Prateek

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