Re: [RFC PATCH v3 00/16] Core scheduling v3

[Phil Auld]

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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