Hello Stefan, folks,

I seem to have another hit, an improvement actually and it seems to be bisected all the way to you, Stefan. Let me use this as another example of how such process could look like and we can use this to hammer-out the details like via what means to submit the request, whom to notify and how to proceed further.

---

Last week I noticed an improvement in TunedLibvirt/fio-rot-Aj-8i/0000:./write-4KiB/throughput/iops_sec.mean (<driver name="qemu" type="raw" io="native" cache="none"/>, fio, rotationary disk, raw file on host xfs partition, jobs=#cpus, iodepth=8, 4k writes) check and bisected it to:

commit fc8796465c6cd4091efe6a2f8b353f07324f49c7
Author: Stefan Hajnoczi <stefanha@redhat.com>
Date:   Wed Feb 23 15:57:03 2022 +0000

    aio-posix: fix spurious ->poll_ready() callbacks in main loop

Could you please confirm that it does make sense and that it is expected? (looks like it from the description).

Note that this commit was pin pointed using 2 out of 3 commits result, there were actually some little differences between commits fc8 and cc5. The fc8 and 202 results scored similarly to both, good and bad commits with 2 being closer to the bad one. Since cc5 they seem to stabilize further scoring slightly lower than the median fc8 result. Anyway I don't have enough data to declare anything. I can bisect it further if needed.

The git bisect log:

git bisect start
# good: [ecf1bbe3227cc1c54d7374aa737e7e0e60ee0c29] Merge tag 'pull-ppc-20220321' of https://github.com/legoater/qemu into staging
git bisect good ecf1bbe3227cc1c54d7374aa737e7e0e60ee0c29
# bad: [9d36d5f7e0dc905d8cb3dd437e479eb536417d3b] Merge tag 'pull-block-2022-03-22' of https://gitlab.com/hreitz/qemu into staging
git bisect bad 9d36d5f7e0dc905d8cb3dd437e479eb536417d3b
# bad: [0f7d7d72aa99c8e48bbbf37262a9c66c83113f76] iotests: use qemu_img_json() when applicable
git bisect bad 0f7d7d72aa99c8e48bbbf37262a9c66c83113f76
# bad: [cc5387a544325c26dcf124ac7d3999389c24e5c6] block/rbd: fix write zeroes with growing images
git bisect bad cc5387a544325c26dcf124ac7d3999389c24e5c6
# good: [b21e2380376c470900fcadf47507f4d5ade75e85] Use g_new() & friends where that makes obvious sense
git bisect good b21e2380376c470900fcadf47507f4d5ade75e85
# bad: [2028ab513bf0232841a909e1368309858919dbcc] Merge tag 'block-pull-request' of https://gitlab.com/stefanha/qemu into staging
git bisect bad 2028ab513bf0232841a909e1368309858919dbcc
# bad: [fc8796465c6cd4091efe6a2f8b353f07324f49c7] aio-posix: fix spurious ->poll_ready() callbacks in main loop
git bisect bad fc8796465c6cd4091efe6a2f8b353f07324f49c7
# good: [8a947c7a586e16a048894e1a0a73d154435e90ef] aio-posix: fix build failure io_uring 2.2
git bisect good 8a947c7a586e16a048894e1a0a73d154435e90ef
# first bad commit: [fc8796465c6cd4091efe6a2f8b353f07324f49c7] aio-posix: fix spurious ->poll_ready() callbacks in main loop

Also please find the bisection report attached. I can attach the VM xml file or other logs if needed.

Regards,
Lukáš


Dne 22. 03. 22 v 16:05 Stefan Hajnoczi napsal(a):
> On Mon, Mar 21, 2022 at 11:29:42AM +0100, Lukáš Doktor wrote:
>> Hello Stefan,
>>
>> Dne 21. 03. 22 v 10:42 Stefan Hajnoczi napsal(a):
>>> On Mon, Mar 21, 2022 at 09:46:12AM +0100, Lukáš Doktor wrote:
>>>> Dear qemu developers,
>>>>
>>>> you might remember the "replied to" email from a bit over year ago to raise a discussion about a qemu performance regression CI. On KVM forum I presented https://www.youtube.com/watch?v=Cbm3o4ACE3Y&list=PLbzoR-pLrL6q4ZzA4VRpy42Ua4-D2xHUR&index=9 some details about my testing pipeline. I think it's stable enough to become part of the official CI so people can consume, rely on it and hopefully even suggest configuration changes.
>>>>
>>>> The CI consists of:
>>>>
>>>> 1. Jenkins pipeline(s) - internal, not available to developers, running daily builds of the latest available commit
>>>> 2. Publicly available anonymized results: https://ldoktor.github.io/tmp/RedHat-Perf-worker1/
>>>
>>> This link is 404.
>>>
>>
>> My mistake, it works well without the tailing slash: https://ldoktor.github.io/tmp/RedHat-Perf-worker1
>>
>>>> 3. (optional) a manual gitlab pulling job which triggered by the Jenkins pipeline when that particular commit is checked
>>>>
>>>> The (1) is described here: https://run-perf.readthedocs.io/en/latest/jenkins.html and can be replicated on other premises and the individual jobs can be executed directly https://run-perf.readthedocs.io on any linux box using Fedora guests (via pip or container https://run-perf.readthedocs.io/en/latest/container.html ).
>>>>
>>>> As for the (3) I made a testing pipeline available here: https://gitlab.com/ldoktor/qemu/-/pipelines with one always-passing test and one allow-to-fail actual testing job. If you think such integration would be useful, I can add it as another job to the official qemu repo. Note the integration is a bit hacky as, due to resources, we can not test all commits but rather test on daily basis, which is not officially supported by gitlab.
>>>>
>>>> Note the aim of this project is to ensure some very basic system-level workflow performance stays the same or that the differences are described and ideally pinned to individual commits. It should not replace thorough release testing or low-level performance tests.
>>>
>>> If I understand correctly the GitLab CI integration you described
>>> follows the "push" model where Jenkins (running on your own machine)
>>> triggers a manual job in GitLab CI simply to indicate the status of the
>>> nightly performance regression test?
>>>
>>> What process should QEMU follow to handle performance regressions
>>> identified by your job? In other words, which stakeholders need to
>>> triage, notify, debug, etc when a regression is identified?
>>>
>>> My guess is:
>>> - Someone (you or the qemu.git committer) need to watch the job status and triage failures.
>>> - That person then notifies likely authors of suspected commits so they can investigate.
>>> - The authors need a way to reproduce the issue - either locally or by pushing commits to GitLab and waiting for test results.
>>> - Fixes will be merged as additional qemu.git commits since commit history cannot be rewritten.
>>> - If necessary a git-revert(1) commit can be merged to temporarily undo a commit that caused issues.
>>>
>>> Who will watch the job status and triage failures?
>>>
>>> Stefan
>>
>> This is exactly the main question I'd like to resolve as part of considering-this-to-be-official-part-of-the-upstream-qemu-testing. At this point our team is offering it's service to maintain this single worker for daily jobs, monitoring the status and pinging people in case of bisectable results.
> 
> That's great! The main hurdle is finding someone to triage regressions
> and if you are volunteering to do that then these regression tests would
> be helpful to QEMU.
> 
>> From the upstream qemu community we are mainly looking for a feedback:
>>
>> * whether they'd want to be notified of such issues (and via what means)
> 
> I have CCed Kevin Wolf in case he has any questions regarding how fio
> regressions will be handled.
> 
> I'm happy to be contacted when a regression bisects to a commit I
> authored.
> 
>> * whether the current approach seems to be actually performing useful tasks
>> * whether the reports are understandable
> 
> Reports aren't something I would look at as a developer. Although the
> history and current status may be useful to some maintainers, that
> information isn't critical. Developers simply need to know which commit
> introduced a regression and the details of how to run the regression.
> 
>> * whether the reports should be regularly pushed into publicly available place (or just on regression/improvement)
>> * whether there are any volunteers to be interested in non-clearly-bisectable issues (probably by-topic)
> 
> One option is to notify maintainers, but when I'm in this position
> myself I usually only investigate critical issues due to limited time.
> 
> Regarding how to contact people, I suggest emailing them and CCing
> qemu-devel so others are aware.
> 
> Thanks,
> Stefan