Re: io_uring_prep_timeout() leading to an IO pressure close to 100

[Jens Axboe]

On 4/1/26 8:59 AM, Fiona Ebner wrote:
> Dear maintainers,
> 
> I'm currently investigating an issue with QEMU causing an IO pressure
> value of nearly 100 when io_uring is used for the event loop of a QEMU
> iothread (which is the case since QEMU 10.2 if io_uring is enabled
> during configuration and available).

It's not "IO pressure", it's the useless iowait metric...

> The cause seems to be the io_uring_prep_timeout() call that is used for
> blocking wait. I attached a minimal reproducer below, which exposes the
> issue [0].
> 
> This was observed on a kernel based on 7.0-rc6 as well as 6.17.13. I
> haven't investigated what happens inside the kernel yet, so I don't know
> if it is an accounting issue or within io_uring.
> 
> Let me know if you need more information or if I should test something
> specific.

If you won't want it, just turn it off with io_uring_set_iowait().

-- 
Jens Axboe