Re: Performance improvement and regression with 6d740fb01b9f0f5ea7a82f4d5e458d91940a19ee

[Lukáš Doktor]

Dne 31. 05. 23 v 19:14 Stefan Hajnoczi napsal(a):
> On Wed, 31 May 2023 at 12:50, Lukáš Doktor <ldoktor@redhat.com> wrote:
>>
>> Dne 26. 05. 23 v 12:56 Stefan Hajnoczi napsal(a):
>>> On Fri, 26 May 2023 at 04:07, Lukáš Doktor <ldoktor@redhat.com> wrote:
>>>>
>>>> Dne 25. 05. 23 v 17:21 Stefan Hajnoczi napsal(a):
>>>>> On Thu, 25 May 2023 at 06:18, Lukáš Doktor <ldoktor@redhat.com> wrote:
>>>>>> the perf-ci detected and bisected the 6d740fb - aio-posix: do not nest 
>>>>>> poll handlers - as a performance improvement when using multiple 
>>>>>> concurrent jobs and 4k (22%) as well as 1024k (63%) blocks on aarch64 
>>>>>> (on a slow rotational disk).
>>>>>>
>>>>>>     
>>>>>> https://ldoktor.github.io/tmp/RedHat-virtlab-arm09/v8.0.0/150-improvement.html
>>>>>>
>>>>>> Based on the commit message I guess it's expected so take this just as a 
>>>>>> record of an improvement.
>>>>>
>>>>> The commit was not intended to change performance and I'm not sure why
>>>>> it happens!
>>>>>
>>>>
>>>> It had and today the x86_64 pipeline finished which shows similar 
>>>> improvement just not in read but rather in write instead and only for 4k 
>>>> blocks (~40%). For 1024k blocks I can see it scoring a bit better (~1.5%). 
>>>> Reads are too jittery to really tell anything on that machine. Anyway I 
>>>> have not done any thorough testing, just a bisection with the most 
>>>> significant setting.
>>>>
>>>> From around the same time I can see a NVMe regression in 4k writes, but 
>>>> first bisection job showed nothing. I'll increase the range and try again 
>>>> as each job since that day shows similar drop.
>>>
>>
>> Hello Stefan, folks,
>>
>> the regression proved to be there and stably reproducible. With NVMe 4k 
>> writes with jobs=10 and iodepth=4 I can see a 50% regression on my machine:
>>
>>     
>> https://ldoktor.github.io/tmp/RedHat-virtlab722/v8.0.0/150-regression.html
>>
>> The rest of the cases doesn't show any change at all. I can provide more 
>> data if someone is interested.
> 
> Which commit caused the regression?

Hello Stefan,

the same one that caused the improvement on rotational disks: 
6d740fb01b9f0f5ea7a82f4d5e458d91940a19ee

Lukáš

> 
> Stefan
>

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