Re: [PATCH 0/2] io_uring/io-wq: respect cgroup cpusets

[Jens Axboe <axboe@kernel.dk>]

On 9/10/24 9:08 AM, MOESSBAUER, Felix wrote:
> On Tue, 2024-09-10 at 08:53 -0600, Jens Axboe wrote:
>> On 9/10/24 8:33 AM, Felix Moessbauer wrote:
>>> Hi,
>>>
>>> this series continues the affinity cleanup work started in
>>> io_uring/sqpoll. It has been tested against the liburing testsuite
>>> (make runtests), whereby the read-mshot test always fails:
>>>
>>>   Running test read-mshot.t
>>>   Buffer ring register failed -22
>>>   test_inc 0 0
>>> failed                                                             
>>>                                                              
>>>   Test read-mshot.t failed with ret 1     
>>>
>>> However, this test also fails on a non-patched linux-next @ 
>>> bc83b4d1f086.
>>
>> That sounds very odd... What liburing are you using? On old kernels
>> where provided buffer rings aren't available the test should just
>> skip,
>> new ones it should pass. Only thing I can think of is that your
>> liburing
>> repo isn't current?
> 
> Hmm... I tested against
> https://github.com/axboe/liburing/commit/74fefa1b51ee35a2014ca6e7667d7c10e9c5b06f

That should certainly be fine.

> I'll redo the test against the unpatched kernel to be 100% sure that it
> is not related to my patches. The -22 is likely an -EINVAL.

I'd be highly surprised if it's related to your patches! Here's what I
get on the current kernel:

axboe@m2max-kvm ~/g/liburing (master)> test/read-mshot.t
axboe@m2max-kvm ~/g/liburing (master)> echo $status
0

and on an older 6.6-stable that doesn't support it:

axboe@m2max-kvm ~/g/liburing (master)> test/read-mshot.t
skip
axboe@m2max-kvm ~/g/liburing (master) [77]> echo $status
77

and then I tried 6.1 since that seems to be your base and get the same
result as 6.6-stable. So not quite sure why it fails on your end, but in
any case, I pushed a commit that I think will sort it for you.

>>> The test wq-aff.t succeeds if at least cpu 0,1 are in the set and
>>> fails otherwise. This is expected, as the test wants to pin on
>>> these
>>> cpus. I'll send a patch for liburing to skip that test in case this
>>> pre-condition is not met.
>>>
>>> Regarding backporting: I would like to backport these patches to
>>> 6.1 as
>>> well, as they affect our realtime applications. However, in-between
>>> 6.1
>>> and next there is a major change da64d6db3bd3 ("io_uring: One wqe
>>> per
>>> wq"), which makes the backport tricky. While I don't think we want
>>> to
>>> backport this change, would a dedicated backport of the two pinning
>>> patches for the old multi-queue implementation have a chance to be
>>> accepted?
>>
>> Let's not backport that patch, just because it's pretty invasive.
>> It's
>> fine to have a separate backport patch of them for -stable, in this
>> case
>> we'll have one version for stable kernels new enough to have that
>> change, and one for older versions. Thankfully not that many to care
>> about.
> 
> Ok, that is fine for me. Then let's first get things right in this
> series and then I'll send the backport.

Exactly, that's the plan. Thanks!

-- 
Jens Axboe