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Message-ID: <2d747fb5-81e7-48ac-ae51-db737a170b81@amd.com>
Date: Fri, 13 Jun 2025 08:58:56 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
juri.lelli@...hat.com, vincent.guittot@...aro.org
Cc: linux-kernel@...r.kernel.org, dietmar.eggemann@....com,
rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
vschneid@...hat.com, clm@...a.com
Subject: Re: [RFC][PATCH 0/5] sched: Try and address some recent-ish
regressions
Hello Peter,
On 6/2/2025 10:14 AM, K Prateek Nayak wrote:
> Hello Peter,
>
> On 5/20/2025 3:15 PM, Peter Zijlstra wrote:
>> As can be seen, the SPR is much easier to please than the SKL for whatever
>> reason. I'm thinking we can make TTWU_QUEUE_DELAYED default on, but I suspect
>> TTWU_QUEUE_DEFAULT might be a harder sell -- we'd need to run more than this
>> one benchmark.
>
> I haven't tried toggling any of the newly added SCHED_FEAT() yet.
Here are the full results:
tldr;
- schbench (old) has a consistent regression for 16, 32, 64,
128, 256 workers (> CCX size, < Overloaded) except for with
256 workers case with TTWU_QUEUE_DEFAULT which shows an
improvement.
- new schebench has few regressions around 32, 64, and 128
workers for wakeup and request latency.
- Most others benchmarks show minor improvements /
regressions but nothing serious.
o Variants
"DELAYED" enables "TTWU_QUEUE_DELAYED" alone, "DEFAULT" enables
"TTWU_QUEUE_DEFAULT" alone, and "BOTH" variant enables both.
vanilla was shared previously which is same as out of box with no
changes made to the sched features.
o Benchmark numbers
==================================================================
Test : hackbench
Units : Normalized time in seconds
Interpretation: Lower is better
Statistic : AMean
==================================================================
Case: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1-groups 1.00 [ -0.00](13.74) 0.92 [ 7.68]( 6.04) 0.95 [ 5.12](10.12) 1.02 [ -1.92]( 6.70) 0.95 [ 4.90]( 5.28)
2-groups 1.00 [ -0.00]( 9.58) 1.04 [ -3.56]( 4.96) 1.03 [ -3.12]( 5.12) 0.98 [ 1.56]( 4.30) 1.01 [ -1.11]( 5.78)
4-groups 1.00 [ -0.00]( 2.10) 1.01 [ -1.30]( 2.27) 1.01 [ -1.09]( 2.68) 1.00 [ -0.43]( 2.58) 1.01 [ -0.65]( 1.38)
8-groups 1.00 [ -0.00]( 1.51) 0.99 [ 1.26]( 1.70) 0.99 [ 0.95]( 4.92) 0.97 [ 3.15]( 1.60) 1.00 [ -0.00]( 3.67)
16-groups 1.00 [ -0.00]( 1.10) 0.97 [ 3.01]( 1.62) 0.96 [ 3.77]( 1.42) 0.95 [ 4.60]( 0.67) 0.96 [ 4.44]( 1.10)
==================================================================
Test : tbench
Units : Normalized throughput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1 1.00 [ 0.00]( 0.82) 1.04 [ 4.33]( 1.84) 1.06 [ 5.97]( 0.42) 1.06 [ 6.12]( 1.02) 1.06 [ 5.54]( 0.73)
2 1.00 [ 0.00]( 1.13) 1.06 [ 5.52]( 1.04) 1.07 [ 7.17]( 0.42) 1.07 [ 6.81]( 0.30) 1.08 [ 7.96]( 0.39)
4 1.00 [ 0.00]( 1.12) 1.05 [ 5.41]( 0.53) 1.07 [ 7.39]( 0.67) 1.06 [ 6.45]( 0.91) 1.07 [ 7.36]( 0.63)
8 1.00 [ 0.00]( 0.93) 1.06 [ 5.72]( 0.47) 1.07 [ 6.90]( 0.24) 1.07 [ 7.09]( 1.45) 1.07 [ 6.94]( 0.45)
16 1.00 [ 0.00]( 0.38) 1.07 [ 6.99]( 0.50) 1.05 [ 4.95]( 0.98) 1.05 [ 5.39]( 0.71) 1.05 [ 5.43]( 1.05)
32 1.00 [ 0.00]( 0.66) 1.05 [ 4.68]( 1.79) 1.06 [ 5.70]( 0.54) 1.07 [ 6.93]( 2.39) 1.03 [ 3.17]( 1.06)
64 1.00 [ 0.00]( 1.18) 1.06 [ 5.53]( 0.37) 1.04 [ 4.05]( 0.84) 1.07 [ 7.35]( 1.57) 1.06 [ 5.62]( 1.13)
128 1.00 [ 0.00]( 1.12) 1.06 [ 5.52]( 0.13) 1.05 [ 4.94]( 0.75) 1.08 [ 7.56]( 0.81) 1.05 [ 4.80]( 0.55)
256 1.00 [ 0.00]( 0.42) 0.99 [ -0.83]( 1.01) 0.99 [ -0.58]( 0.57) 1.00 [ 0.06]( 0.68) 1.00 [ 0.03]( 1.47)
512 1.00 [ 0.00]( 0.14) 1.01 [ 1.06]( 0.13) 1.02 [ 1.67]( 0.18) 1.03 [ 2.62]( 0.28) 1.02 [ 2.17]( 0.33)
1024 1.00 [ 0.00]( 0.26) 1.02 [ 1.82]( 0.41) 1.02 [ 2.48]( 0.27) 1.03 [ 3.38]( 0.37) 1.01 [ 1.39]( 0.03)
==================================================================
Test : stream-10
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
Copy 1.00 [ 0.00]( 8.37) 0.97 [ -2.79]( 9.17) 0.99 [ -1.29]( 4.68) 1.01 [ 1.25]( 4.86) 0.99 [ -0.66]( 9.29)
Scale 1.00 [ 0.00]( 2.85) 1.00 [ 0.12]( 2.91) 0.99 [ -1.34]( 5.55) 1.00 [ -0.20]( 3.38) 0.98 [ -2.09]( 5.33)
Add 1.00 [ 0.00]( 3.39) 0.98 [ -2.36]( 4.85) 0.98 [ -2.32]( 5.23) 1.00 [ 0.10]( 3.17) 0.98 [ -1.99]( 4.73)
Triad 1.00 [ 0.00]( 6.39) 1.01 [ 1.45]( 8.42) 1.00 [ -0.38]( 8.28) 1.05 [ 4.69]( 5.66) 1.06 [ 6.02]( 4.53)
==================================================================
Test : stream-100
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
Copy 1.00 [ 0.00]( 3.91) 0.98 [ -1.84]( 2.07) 0.98 [ -2.06]( 6.75) 1.01 [ 1.31]( 2.86) 1.02 [ 2.12]( 3.30)
Scale 1.00 [ 0.00]( 4.34) 0.96 [ -3.80]( 6.38) 0.97 [ -2.88]( 6.99) 0.97 [ -2.62]( 5.70) 1.00 [ -0.37]( 3.94)
Add 1.00 [ 0.00]( 4.14) 0.97 [ -3.04]( 6.31) 0.97 [ -3.14]( 6.91) 0.99 [ -0.79]( 4.24) 1.00 [ -0.35]( 4.06)
Triad 1.00 [ 0.00]( 1.00) 0.98 [ -2.36]( 2.60) 0.96 [ -3.80]( 6.15) 0.99 [ -0.61]( 1.33) 0.97 [ -3.05]( 5.48)
==================================================================
Test : netperf
Units : Normalized Througput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1-clients 1.00 [ 0.00]( 0.41) 1.06 [ 5.63]( 1.17) 1.06 [ 6.03]( 0.53) 1.09 [ 8.63]( 0.79) 1.06 [ 6.36]( 0.09)
2-clients 1.00 [ 0.00]( 0.58) 1.06 [ 6.25]( 0.85) 1.05 [ 5.47]( 0.83) 1.08 [ 8.24]( 1.29) 1.05 [ 5.15]( 0.57)
4-clients 1.00 [ 0.00]( 0.35) 1.06 [ 5.59]( 0.49) 1.05 [ 5.06]( 0.65) 1.08 [ 8.15]( 0.82) 1.05 [ 5.46]( 0.62)
8-clients 1.00 [ 0.00]( 0.48) 1.06 [ 5.76]( 0.81) 1.05 [ 5.26]( 0.71) 1.08 [ 8.19]( 0.60) 1.05 [ 5.34]( 0.80)
16-clients 1.00 [ 0.00]( 0.66) 1.06 [ 5.95]( 0.69) 1.06 [ 5.52]( 0.78) 1.08 [ 8.31]( 0.86) 1.06 [ 5.76]( 0.48)
32-clients 1.00 [ 0.00]( 1.15) 1.06 [ 5.84]( 1.34) 1.06 [ 5.57]( 0.96) 1.08 [ 8.30]( 0.90) 1.06 [ 5.66]( 1.45)
64-clients 1.00 [ 0.00]( 1.38) 1.05 [ 5.20]( 1.50) 1.05 [ 4.67]( 1.39) 1.07 [ 7.43]( 1.47) 1.05 [ 5.18]( 1.48)
128-clients 1.00 [ 0.00]( 0.87) 1.04 [ 4.39]( 1.03) 1.04 [ 4.43]( 0.98) 1.06 [ 5.98]( 1.01) 1.05 [ 4.60]( 1.06)
256-clients 1.00 [ 0.00]( 5.36) 1.00 [ 0.10]( 3.48) 1.00 [ 0.09]( 4.22) 1.01 [ 0.71]( 3.18) 1.01 [ 1.25]( 3.69)
512-clients 1.00 [ 0.00](54.39) 0.98 [ -1.93](52.45) 1.00 [ -0.35](53.30) 1.02 [ 1.75](54.93) 1.02 [ 1.76](55.71)
==================================================================
Test : schbench
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1 1.00 [ -0.00]( 8.54) 0.89 [ 10.87](35.39) 0.78 [ 21.74](34.41) 0.91 [ 8.70](12.44) 0.72 [ 28.26](26.70)
2 1.00 [ -0.00]( 1.15) 0.88 [ 12.00]( 4.55) 0.78 [ 22.00]( 6.61) 0.90 [ 10.00]( 5.75) 0.82 [ 18.00](17.98)
4 1.00 [ -0.00](13.46) 0.96 [ 4.17](10.60) 1.00 [ -0.00]( 8.54) 0.96 [ 4.17]( 3.30) 0.98 [ 2.08]( 8.19)
8 1.00 [ -0.00]( 7.14) 0.84 [ 15.79]( 8.44) 0.98 [ 1.75]( 3.67) 0.95 [ 5.26]( 4.99) 0.91 [ 8.77]( 2.92)
16 1.00 [ -0.00]( 3.49) 1.08 [ -8.47]( 4.69) 1.07 [ -6.78]( 0.92) 1.07 [ -6.78]( 0.91) 1.07 [ -6.78]( 3.27)
32 1.00 [ -0.00]( 1.06) 1.10 [ -9.57]( 2.91) 1.07 [ -7.45]( 2.97) 1.07 [ -7.45]( 4.23) 1.05 [ -5.32]( 7.80)
64 1.00 [ -0.00]( 5.48) 1.25 [-25.00]( 5.36) 1.17 [-17.44]( 1.44) 1.23 [-23.26]( 2.79) 1.20 [-19.77]( 2.19)
128 1.00 [ -0.00](10.45) 1.18 [-17.99](12.54) 1.16 [-16.36](21.21) 1.13 [-12.85](12.71) 1.09 [ -8.64]( 3.05)
256 1.00 [ -0.00](31.14) 1.28 [-27.79](17.66) 0.84 [ 16.21](32.14) 1.19 [-19.21]( 1.68) 1.07 [ -6.86]( 7.48)
512 1.00 [ -0.00]( 1.52) 1.01 [ -0.51]( 2.78) 0.97 [ 3.03]( 2.91) 0.98 [ 1.77]( 1.07) 1.01 [ -0.51]( 1.01)
==================================================================
Test : new-schbench-requests-per-second
Units : Normalized Requests per second
Interpretation: Higher is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1 1.00 [ 0.00]( 1.07) 1.00 [ 0.29]( 0.00) 1.00 [ 0.29]( 0.15) 0.99 [ -0.59]( 0.46) 1.00 [ 0.29]( 0.30)
2 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00)
4 1.00 [ 0.00]( 0.00) 1.00 [ -0.29]( 0.15) 1.00 [ 0.00]( 0.00) 1.00 [ -0.29]( 0.15) 1.00 [ 0.00]( 0.00)
8 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.15) 1.00 [ 0.29]( 0.00) 1.00 [ 0.00]( 0.40) 1.00 [ 0.29]( 0.15)
16 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.00)
32 1.00 [ 0.00]( 3.41) 0.99 [ -0.95]( 2.06) 0.98 [ -2.23]( 3.41) 0.98 [ -2.23]( 3.31) 1.03 [ 2.54]( 0.32)
64 1.00 [ 0.00]( 1.05) 0.92 [ -7.58]( 9.01) 0.86 [-13.92](11.30) 1.00 [ 0.00]( 4.74) 1.00 [ -0.38]( 9.98)
128 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00) 1.00 [ 0.38]( 0.00)
256 1.00 [ 0.00]( 0.72) 1.00 [ -0.31]( 0.42) 1.01 [ 1.23]( 1.33) 1.01 [ 0.61]( 0.83) 1.01 [ 0.92]( 1.36)
512 1.00 [ 0.00]( 0.57) 1.00 [ 0.00]( 0.45) 0.99 [ -0.72]( 1.18) 1.00 [ 0.48]( 0.33) 1.01 [ 1.44]( 0.49)
==================================================================
Test : new-schbench-wakeup-latency
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1 1.00 [ -0.00]( 9.11) 0.75 [ 25.00](11.08) 0.69 [ 31.25]( 8.13) 0.75 [ 25.00](11.08) 0.62 [ 37.50]( 8.94)
2 1.00 [ -0.00]( 0.00) 1.00 [ -0.00]( 3.78) 0.86 [ 14.29]( 7.45) 0.93 [ 7.14]( 3.87) 0.79 [ 21.43]( 4.84)
4 1.00 [ -0.00]( 3.78) 0.93 [ 7.14]( 3.87) 0.79 [ 21.43]( 4.56) 0.93 [ 7.14]( 0.00) 0.79 [ 21.43]( 8.85)
8 1.00 [ -0.00]( 0.00) 1.08 [ -8.33](12.91) 0.92 [ 8.33]( 0.00) 0.83 [ 16.67](18.23) 1.08 [ -8.33](12.91)
16 1.00 [ -0.00]( 7.56) 0.92 [ 7.69](11.71) 0.85 [ 15.38](12.06) 1.08 [ -7.69](11.92) 0.85 [ 15.38](12.91)
32 1.00 [ -0.00](15.11) 1.07 [ -6.67]( 3.30) 1.00 [ -0.00](19.06) 1.00 [ -0.00](15.11) 0.80 [ 20.00]( 4.43)
64 1.00 [ -0.00]( 9.63) 1.00 [ -0.00]( 8.15) 1.00 [ -0.00]( 5.34) 1.05 [ -5.00]( 7.75) 0.90 [ 10.00]( 9.94)
128 1.00 [ -0.00]( 4.86) 0.89 [ 11.06]( 7.83) 0.91 [ 8.54]( 7.87) 0.88 [ 12.06]( 8.73) 0.86 [ 14.07]( 5.01)
256 1.00 [ -0.00]( 2.34) 1.00 [ 0.20]( 0.10) 1.04 [ -4.50]( 4.59) 1.03 [ -2.90]( 1.95) 1.04 [ -3.70]( 4.13)
512 1.00 [ -0.00]( 0.40) 1.00 [ 0.38]( 0.20) 1.00 [ 0.38]( 0.20) 0.99 [ 0.77]( 0.20) 1.00 [ -0.00]( 0.40)
==================================================================
Test : new-schbench-request-latency
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) vanilla[pct imp](CV) DELAYED[pct imp](CV) DEFUALT[pct imp](CV) BOTH[pct imp](CV)
1 1.00 [ -0.00]( 2.73) 0.98 [ 2.08]( 1.04) 0.99 [ 1.30]( 1.07) 1.02 [ -1.82]( 0.00) 1.01 [ -1.30]( 3.10)
2 1.00 [ -0.00]( 0.87) 1.05 [ -5.40]( 3.10) 1.02 [ -1.89]( 1.58) 1.01 [ -1.08]( 2.76) 1.02 [ -1.62]( 1.45)
4 1.00 [ -0.00]( 1.21) 0.99 [ 0.54]( 1.27) 0.99 [ 1.08]( 1.67) 1.01 [ -1.21]( 1.21) 1.01 [ -1.35]( 1.91)
8 1.00 [ -0.00]( 0.27) 0.99 [ 0.79]( 2.14) 0.98 [ 2.37]( 0.72) 0.99 [ 1.05]( 2.53) 0.99 [ 0.79]( 1.12)
16 1.00 [ -0.00]( 4.04) 1.01 [ -0.53]( 0.55) 1.01 [ -0.80]( 1.08) 1.00 [ -0.27]( 0.36) 0.99 [ 0.53]( 0.50)
32 1.00 [ -0.00]( 7.35) 1.10 [ -9.97](21.10) 1.01 [ -0.66](10.27) 1.25 [-25.36](21.41) 0.90 [ 9.52]( 2.08)
64 1.00 [ -0.00]( 3.54) 1.03 [ -2.89]( 1.55) 1.02 [ -2.00]( 0.98) 1.01 [ -0.67]( 3.62) 1.01 [ -0.89]( 4.98)
128 1.00 [ -0.00]( 0.37) 0.99 [ 0.62]( 0.00) 0.99 [ 0.72]( 0.11) 0.99 [ 0.62]( 0.11) 0.99 [ 0.83]( 0.11)
256 1.00 [ -0.00]( 9.57) 0.92 [ 8.36]( 2.22) 1.03 [ -3.11](12.58) 1.05 [ -5.02]( 8.36) 1.00 [ -0.00](11.71)
512 1.00 [ -0.00]( 1.82) 1.01 [ -1.23]( 0.94) 1.02 [ -2.45]( 1.53) 1.00 [ 0.35]( 0.83) 1.02 [ -1.93]( 1.40)
==================================================================
Test : Various longer running benchmarks
Units : %diff in throughput reported
Interpretation: Higher is better
Statistic : Median
==================================================================
Benchmarks: vanilla DELAYED DEFAULT BOTH
ycsb-cassandra -0.05% 0.65% -0.49% -0.48%
ycsb-mongodb -0.80% -0.85% -1.00% -0.98%
deathstarbench-1x 2.44% 1.54% 1.65% 0.18%
deathstarbench-2x 5.47% 4.88% 7.92% 6.75%
deathstarbench-3x 0.36% 1.74% -1.75% 0.31%
deathstarbench-6x 1.14% 1.94% 2.24% 1.58%
hammerdb+mysql 16VU 1.08% 5.21% 2.69% 3.80%
hammerdb+mysql 64VU -0.43% -0.31% 2.12% -0.25%
--
Thanks and Regards,
Prateek
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