From: Jens Axboe <axboe@kernel.dk>
To: Fiona Ebner <f.ebner@proxmox.com>, linux-kernel@vger.kernel.org
Cc: hannes@cmpxchg.org, surenb@google.com, peterz@infradead.org,
io-uring@vger.kernel.org
Subject: Re: io_uring_prep_timeout() leading to an IO pressure close to 100
Date: Wed, 1 Apr 2026 09:03:43 -0600 [thread overview]
Message-ID: <49a977f3-45da-41dd-9fd6-75fd6760a591@kernel.dk> (raw)
In-Reply-To: <14bc6266-5bc9-4454-9518-d1016bfe417b@proxmox.com>
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
next prev parent reply other threads:[~2026-04-01 15:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-01 14:59 io_uring_prep_timeout() leading to an IO pressure close to 100 Fiona Ebner
2026-04-01 15:03 ` Jens Axboe [this message]
2026-04-02 9:12 ` Fiona Ebner
2026-04-02 12:31 ` Fiona Ebner
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