Re: Performance improvement with 6d740fb01b9f0f5ea7a82f4d5e458d91940a19ee

[Lukáš Doktor]

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.

Regards,
Lukáš

> Thanks!
> 
> Stefan
>

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