Re: [PATCH 2/2] io_uring: switch local task_work to a mpscq

[Jens Axboe <axboe@kernel.dk>]

On 6/12/26 6:21 AM, Jens Axboe wrote:
> On 6/11/26 11:24 PM, Caleb Sander Mateos wrote:
>> On Thu, Jun 11, 2026 at 7:23?PM Jens Axboe <axboe@kernel.dk> wrote:
>>>
>>> On 6/11/26 7:14 PM, Caleb Sander Mateos wrote:
>>>> This is great stuff! I had also observed these hotspots on a ublk
>>>> workload. Since incoming ublk requests post task work to the ublk
>>>> server's io_urings and completed ublk requests post task work to the
>>>> client's io_urings, there is significant cross-CPU contention on the
>>>> task work queues.
>>>
>>> Glad you like it! Once I post v2 tomorrow, perhaps you can try and run
>>> some tests with and without and see how it does for you?
>>
>> Haven't tested v2 yet, but v1 shows a 4% IOPS improvement on a ublk
>> 4-KB read workload. The workload has 8 CPUs (unpaired hypertwins)
>> running fio with io_uring submitting I/O to the ublk devices and 32
>> ublk server CPUs (paired hypertwins) servicing the requests, achieving
>> around 4M IOPS. Both the client and server CPUs look completely busy.
> 
> That's a pretty nice improvement! Would be curious to hear what v2 looks
> like.

And here's some more stuff on top you might find interesting. For a
6 NVMe drive test, it drops my task work usage from top-of-profiles
to ~2%.

https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git/log/?h=io_uring-tw-mpscq-batch

The patches sit on top of the io_uring-tw-mpscq branch.

-- 
Jens Axboe