Re: [PATCH 0/6 v2] sched/eevdf: Improve scheduling latency of short slice task
From: K Prateek Nayak
Date: Tue Jun 16 2026 - 03:44:14 EST
Hello Vincent,
On 6/15/2026 9:54 PM, Vincent Guittot wrote:
> This series continues to improve the scheduling latency of tasks with
> shorter slice duration by mainly canceling, updating or minimizing the
> protection of the running tasks when appropriate.
>
> Benchmarks, like hackbench, haven't seen any noticeable performance
> differences with this patchset (The default 2.8ms slice has been used for
> testing performance regressions)
I've left a few comments on the thread but for the vanilla runs, I too
can confirm there aren't any without any slice tuning.
Following are results from a dual socket 4th Generation EPYC system
(2 x 128C/256T) with the series applied on top of
"sched-core-2026-06-14":
==================================================================
Test : hackbench
Units : Normalized time in seconds
Interpretation: Lower is better
Statistic : AMean
==================================================================
Case: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1-groups 1.00 [ -0.00]( 9.66) 0.86 [ 14.32](14.00)
2-groups 1.00 [ -0.00]( 9.22) 1.02 [ -1.78](10.45)
4-groups 1.00 [ -0.00]( 2.14) 0.98 [ 2.33]( 1.99)
8-groups 1.00 [ -0.00]( 2.80) 0.97 [ 2.88]( 2.93)
16-groups 1.00 [ -0.00]( 5.54) 1.00 [ 0.49]( 2.58)
==================================================================
Test : tbench
Units : Normalized throughput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1 1.00 [ 0.00]( 0.03) 1.00 [ 0.36]( 0.20)
2 1.00 [ 0.00]( 0.32) 1.00 [ 0.09]( 0.14)
4 1.00 [ 0.00]( 0.34) 1.00 [ 0.39]( 0.28)
8 1.00 [ 0.00]( 0.24) 1.00 [ 0.01]( 0.24)
16 1.00 [ 0.00]( 0.45) 1.00 [ 0.01]( 0.47)
32 1.00 [ 0.00]( 0.58) 1.01 [ 0.75]( 0.30)
64 1.00 [ 0.00]( 0.81) 1.02 [ 1.62]( 0.62)
128 1.00 [ 0.00]( 0.53) 1.03 [ 3.24]( 0.25)
256 1.00 [ 0.00]( 0.30) 1.00 [ 0.39]( 0.26)
512 1.00 [ 0.00]( 3.73) 1.01 [ 1.47]( 1.13)
1024 1.00 [ 0.00]( 0.23) 1.00 [ -0.10]( 0.37)
2048 1.00 [ 0.00]( 0.14) 1.00 [ 0.29]( 0.19)
==================================================================
Test : stream-10
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
Copy 1.00 [ 0.00]( 0.66) 0.99 [ -0.70]( 1.66)
Scale 1.00 [ 0.00]( 0.89) 0.99 [ -0.77]( 1.52)
Add 1.00 [ 0.00]( 0.73) 1.00 [ -0.34]( 1.31)
Triad 1.00 [ 0.00]( 0.70) 0.99 [ -0.52]( 1.24)
==================================================================
Test : stream-100
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
Copy 1.00 [ 0.00]( 0.32) 1.00 [ 0.07]( 0.36)
Scale 1.00 [ 0.00]( 0.26) 1.00 [ -0.00]( 0.45)
Add 1.00 [ 0.00]( 0.29) 1.00 [ -0.05]( 0.39)
Triad 1.00 [ 0.00]( 0.27) 1.00 [ -0.05]( 0.37)
==================================================================
Test : netperf
Units : Normalized Througput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1-clients 1.00 [ 0.00]( 0.10) 1.00 [ 0.02]( 0.19)
2-clients 1.00 [ 0.00]( 0.29) 1.00 [ 0.02]( 0.18)
4-clients 1.00 [ 0.00]( 0.36) 1.00 [ -0.01]( 0.23)
8-clients 1.00 [ 0.00]( 0.32) 1.00 [ 0.04]( 0.22)
16-clients 1.00 [ 0.00]( 0.24) 1.00 [ 0.09]( 0.22)
32-clients 1.00 [ 0.00]( 0.42) 1.00 [ 0.30]( 0.33)
64-clients 1.00 [ 0.00]( 0.94) 1.00 [ 0.48]( 0.67)
128-clients 1.00 [ 0.00]( 1.10) 1.01 [ 0.77]( 1.31)
256-clients 1.00 [ 0.00]( 1.06) 1.02 [ 2.02]( 1.18)
512-clients 1.00 [ 0.00]( 4.68) 0.99 [ -1.14]( 5.63)
768-clients 1.00 [ 0.00](34.35) 0.99 [ -1.00](34.84)
1024-clients 1.00 [ 0.00](42.76) 0.99 [ -0.81](45.77)
==================================================================
Test : schbench
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1 1.00 [ -0.00](18.94) 0.39 [ 61.36]( 5.88)
2 1.00 [ -0.00]( 1.67) 0.91 [ 8.57]( 6.64)
4 1.00 [ -0.00]( 9.79) 0.84 [ 16.22]( 7.78)
8 1.00 [ -0.00]( 2.27) 0.89 [ 11.36](10.54)
16 1.00 [ -0.00]( 0.00) 0.98 [ 1.79]( 4.10)
32 1.00 [ -0.00]( 1.92) 1.01 [ -1.25]( 0.72)
64 1.00 [ -0.00]( 1.19) 1.01 [ -0.78]( 1.18)
128 1.00 [ -0.00]( 0.67) 1.01 [ -1.32]( 0.25)
256 1.00 [ -0.00]( 0.46) 1.03 [ -3.08]( 4.37)
512 1.00 [ -0.00]( 0.33) 1.01 [ -0.66]( 0.38)
768 1.00 [ -0.00]( 4.69) 1.02 [ -1.55](10.18)
1024 1.00 [ -0.00]( 2.71) 1.00 [ -0.00]( 4.43)
==================================================================
Test : new-schbench-requests-per-second
Units : Normalized Requests per second
Interpretation: Higher is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1 1.00 [ 0.00]( 0.15) 0.99 [ -0.59]( 0.15)
2 1.00 [ 0.00]( 0.00) 0.99 [ -0.59]( 0.15)
4 1.00 [ 0.00]( 0.00) 0.99 [ -0.88]( 0.31)
8 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.00)
16 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.00)
32 1.00 [ 0.00]( 0.15) 1.00 [ 0.00]( 0.15)
64 1.00 [ 0.00]( 0.00) 1.00 [ 0.00]( 0.00)
128 1.00 [ 0.00](12.53) 0.98 [ -1.77](15.94)
256 1.00 [ 0.00]( 0.15) 0.99 [ -0.85]( 0.39)
512 1.00 [ 0.00]( 0.84) 1.00 [ 0.00]( 0.84)
768 1.00 [ 0.00]( 2.05) 0.99 [ -0.94]( 1.94)
1024 1.00 [ 0.00]( 2.90) 1.01 [ 1.35]( 2.18)
==================================================================
Test : new-schbench-wakeup-latency
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1 1.00 [ -0.00](12.99) 1.47 [-46.67](27.72)
2 1.00 [ -0.00]( 4.08) 0.85 [ 15.38]( 0.00)
4 1.00 [ -0.00]( 0.00) 0.82 [ 18.18]( 0.00)
8 1.00 [ -0.00]( 0.00) 1.27 [-27.27]( 3.78)
16 1.00 [ -0.00]( 4.56) 1.27 [-27.27]( 0.00)
32 1.00 [ -0.00]( 0.00) 1.00 [ -0.00]( 4.56)
64 1.00 [ -0.00]( 5.00) 1.00 [ -0.00]( 5.00)
128 1.00 [ -0.00]( 7.45) 1.25 [-25.00](14.68)
256 1.00 [ -0.00]( 2.70) 0.96 [ 4.48]( 8.12)
512 1.00 [ -0.00]( 0.00) 1.00 [ -0.00]( 0.00)
768 1.00 [ -0.00]( 1.66) 1.01 [ -1.47]( 2.52)
1024 1.00 [ -0.00]( 3.32) 1.01 [ -0.59]( 0.66)
Note: The absolute numbers are very small until 256 threads (~10-15us)
which may causes a small variation to appear as a large regression.
==================================================================
Test : new-schbench-request-latency
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) preempt_short_opt[pct imp](CV)
1 1.00 [ -0.00]( 0.14) 1.01 [ -1.06]( 0.27)
2 1.00 [ -0.00]( 0.14) 1.02 [ -1.60]( 0.23)
4 1.00 [ -0.00]( 0.00) 1.05 [ -4.53]( 1.73)
8 1.00 [ -0.00]( 0.14) 1.01 [ -0.53]( 0.14)
16 1.00 [ -0.00]( 1.49) 1.00 [ -0.26]( 1.23)
32 1.00 [ -0.00]( 0.89) 1.01 [ -0.79]( 0.00)
64 1.00 [ -0.00]( 1.43) 1.00 [ -0.26]( 0.98)
128 1.00 [ -0.00]( 2.78) 1.01 [ -1.18]( 4.09)
256 1.00 [ -0.00]( 0.13) 1.00 [ -0.25]( 0.26)
512 1.00 [ -0.00]( 6.72) 1.02 [ -2.20]( 5.45)
768 1.00 [ -0.00]( 3.42) 1.01 [ -0.52]( 4.21)
1024 1.00 [ -0.00]( 4.37) 1.01 [ -1.19]( 2.15)
>
> Several use cases has been used to testing the scheduling latency of short
> slice tasks:
> - cyclictest with a 3777us period and a 8ms slice alone
> - cyclictest with a 3777us period and a 8ms slice. 2xNR_CPUS rt-app
> tasks that run (8177us) and sleep (17777us) with a 16ms slice.
> - cyclictest with a 3777us period and a 8ms slice. Hackbench with
> 1 group using thread and pipe and a 16ms slice.
I'll go check those configurations next and report back if I find
anything out of the ordinary. Feel free to include:
Tested-by: K Prateek Nayak <kprateek.nayak@xxxxxxx>
--
Thanks and Regards,
Prateek