Re: [PATCH 6.4 800/800] io_uring: Use io_schedule* in cqring wait

[Linux regression tracking #adding (Thorsten Leemhuis)]

[CCing the regression list, as it should be in the loop for regressions:
https://docs.kernel.org/admin-guide/reporting-regressions.html]

[TLDR: I'm adding this report to the list of tracked Linux kernel
regressions; the text you find below is based on a few templates
paragraphs you might have encountered already in similar form.
See link in footer if these mails annoy you.]

On 23.07.23 11:39, Oleksandr Natalenko wrote:
> On neděle 16. července 2023 21:50:53 CEST Greg Kroah-Hartman wrote:
>> From: Andres Freund <andres@xxxxxxxxxxx>
>>
>> commit 8a796565cec3601071cbbd27d6304e202019d014 upstream.
>>
>> I observed poor performance of io_uring compared to synchronous IO. That
>> turns out to be caused by deeper CPU idle states entered with io_uring,
>> due to io_uring using plain schedule(), whereas synchronous IO uses
>> io_schedule().
>>
>> The losses due to this are substantial. On my cascade lake workstation,
>> t/io_uring from the fio repository e.g. yields regressions between 20%
>> and 40% with the following command:
>> ./t/io_uring -r 5 -X0 -d 1 -s 1 -c 1 -p 0 -S$use_sync -R 0 /mnt/t2/fio/write.0.0
>>
> 
> Reportedly, this caused a regression as reported in [1] [2] [3]. Not only v6.4.4 is affected, v6.1.39 is affected too.
> 
> Reverting this commit fixes the issue.
> 
> Please check.
> 
> Thanks.
> 
> [1] https://bbs.archlinux.org/viewtopic.php?id=287343
> [2] https://bugzilla.kernel.org/show_bug.cgi?id=217700
> [3] https://bugzilla.kernel.org/show_bug.cgi?id=217699

Thanks for the report. To be sure the issue doesn't fall through the
cracks unnoticed, I'm adding it to regzbot, the Linux kernel regression
tracking bot:

#regzbot introduced 8a796565cec360107 ^
https://bbs.archlinux.org/viewtopic.php?id=287343
https://bugzilla.kernel.org/show_bug.cgi?id=217700
https://bugzilla.kernel.org/show_bug.cgi?id=217699
#regzbot title block: io_uring: high iowait rates and stalls
#regzbot ignore-activity

This isn't a regression? This issue or a fix for it are already
discussed somewhere else? It was fixed already? You want to clarify when
the regression started to happen? Or point out I got the title or
something else totally wrong? Then just reply and tell me -- ideally
while also telling regzbot about it, as explained by the page listed in
the footer of this mail.

Developers: When fixing the issue, remember to add 'Link:' tags pointing
to the report (the parent of this mail). See page linked in footer for
details.

Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)
--
Everything you wanna know about Linux kernel regression tracking:
https://linux-regtracking.leemhuis.info/about/#tldr
That page also explains what to do if mails like this annoy you.