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SubjectRe: [RFC PATCH v3 00/16] Core scheduling v3
Hi,

On Fri, Aug 02, 2019 at 11:37:15AM -0400 Julien Desfossez wrote:
> We tested both Aaron's and Tim's patches and here are our results.
>
> Test setup:
> - 2 1-thread sysbench, one running the cpu benchmark, the other one the
> mem benchmark
> - both started at the same time
> - both are pinned on the same core (2 hardware threads)
> - 10 30-seconds runs
> - test script: https://paste.debian.net/plainh/834cf45c
> - only showing the CPU events/sec (higher is better)
> - tested 4 tag configurations:
> - no tag
> - sysbench mem untagged, sysbench cpu tagged
> - sysbench mem tagged, sysbench cpu untagged
> - both tagged with a different tag
> - "Alone" is the sysbench CPU running alone on the core, no tag
> - "nosmt" is both sysbench pinned on the same hardware thread, no tag
> - "Tim's full patchset + sched" is an experiment with Tim's patchset
> combined with Aaron's "hack patch" to get rid of the remaining deep
> idle cases
> - In all test cases, both tasks can run simultaneously (which was not
> the case without those patches), but the standard deviation is a
> pretty good indicator of the fairness/consistency.
>
> No tag
> ------
> Test Average Stdev
> Alone 1306.90 0.94
> nosmt 649.95 1.44
> Aaron's full patchset: 828.15 32.45
> Aaron's first 2 patches: 832.12 36.53
> Aaron's 3rd patch alone: 864.21 3.68
> Tim's full patchset: 852.50 4.11
> Tim's full patchset + sched: 852.59 8.25
>
> Sysbench mem untagged, sysbench cpu tagged
> ------------------------------------------
> Test Average Stdev
> Alone 1306.90 0.94
> nosmt 649.95 1.44
> Aaron's full patchset: 586.06 1.77
> Aaron's first 2 patches: 630.08 47.30
> Aaron's 3rd patch alone: 1086.65 246.54
> Tim's full patchset: 852.50 4.11
> Tim's full patchset + sched: 390.49 15.76
>
> Sysbench mem tagged, sysbench cpu untagged
> ------------------------------------------
> Test Average Stdev
> Alone 1306.90 0.94
> nosmt 649.95 1.44
> Aaron's full patchset: 583.77 3.52
> Aaron's first 2 patches: 513.63 63.09
> Aaron's 3rd patch alone: 1171.23 3.35
> Tim's full patchset: 564.04 58.05
> Tim's full patchset + sched: 1026.16 49.43
>
> Both sysbench tagged
> --------------------
> Test Average Stdev
> Alone 1306.90 0.94
> nosmt 649.95 1.44
> Aaron's full patchset: 582.15 3.75
> Aaron's first 2 patches: 561.07 91.61
> Aaron's 3rd patch alone: 638.49 231.06
> Tim's full patchset: 679.43 70.07
> Tim's full patchset + sched: 664.34 210.14
>

Sorry if I'm missing something obvious here but with only 2 processes
of interest shouldn't one tagged and one untagged be about the same
as both tagged?

In both cases the 2 sysbenches should not be running on the core at
the same time.

There will be times when oher non-related threads could share the core
with the untagged one. Is that enough to account for this difference?


Thanks,
Phil


> So in terms of fairness, Aaron's full patchset is the most consistent, but only
> Tim's patchset performs better than nosmt in some conditions.
>
> Of course, this is one of the worst case scenario, as soon as we have
> multithreaded applications on overcommitted systems, core scheduling performs
> better than nosmt.
>
> Thanks,
>
> Julien

--

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