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Wed, 01 Apr 2026 08:03:44 -0700 (PDT) Message-ID: <49a977f3-45da-41dd-9fd6-75fd6760a591@kernel.dk> Date: Wed, 1 Apr 2026 09:03:43 -0600 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: io_uring_prep_timeout() leading to an IO pressure close to 100 To: Fiona Ebner , linux-kernel@vger.kernel.org Cc: hannes@cmpxchg.org, surenb@google.com, peterz@infradead.org, io-uring@vger.kernel.org References: <14bc6266-5bc9-4454-9518-d1016bfe417b@proxmox.com> Content-Language: en-US From: Jens Axboe In-Reply-To: <14bc6266-5bc9-4454-9518-d1016bfe417b@proxmox.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit 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