Re: Performance improvement with 6d740fb01b9f0f5ea7a82f4d5e458d91940a19ee

[Stefan Hajnoczi]

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?

Stefan