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

[Aaron Lu]

On 2019/8/6 22:17, Phil Auld wrote:
> On Tue, Aug 06, 2019 at 09:54:01PM +0800 Aaron Lu wrote:
>> On Mon, Aug 05, 2019 at 04:09:15PM -0400, Phil Auld wrote:
>>> 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?  
>>
>> It should.
>>
>>> In both cases the 2 sysbenches should not be running on the core at 
>>> the same time. 
>>
>> Agree.
>>
>>> 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?
>>
>> What difference do you mean?
> 
> 
> I was looking at the above posted numbers. For example:
> 
>>>> Sysbench mem untagged, sysbench cpu tagged
>>>> Aaron's 3rd patch alone:        1086.65     246.54
> 
>>>> Sysbench mem tagged, sysbench cpu untagged
>>>> Aaron's 3rd patch alone:        1171.23     3.35
> 
>>>> Both sysbench tagged
>>>> Aaron's 3rd patch alone:        638.49      231.06
> 
> 
> Admittedly, there's some high variance on some of those numbers. 

The high variance suggests the code having some fairness issues :-)

For the test here, I didn't expect the 3rd patch being used alone
since the fairness is solved by patch2 and patch3 together.