From: Keith Busch <kbusch@kernel.org>
To: Teng Qin <palmtenor@gmail.com>
Cc: Yu Kuai <yukuai1@huaweicloud.com>,
linux-block@vger.kernel.org, hch@lst.de, axboe@kernel.dk,
sagi@grimberg.me, "yukuai (C)" <yukuai3@huawei.com>
Subject: Re: Question on setting IO polling behavior and documentations
Date: Fri, 15 Aug 2025 21:59:21 -0600 [thread overview]
Message-ID: <aKACGfROBeAGixs0@kbusch-mbp> (raw)
In-Reply-To: <CAHumS0Ddg7wj50jvoR1Z9dJrXeizz+=4k7Az0qB_9QH-tAhvQA@mail.gmail.com>
On Thu, Aug 14, 2025 at 06:35:01PM -0400, Teng Qin wrote:
> On Thu, Aug 14, 2025 at 5:31 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
> >
> > Hi,
> >
> > 在 2025/08/14 13:14, Teng Qin 写道:
> >> Moreover, the block layer documentation at
> >> Documentation/ABI/stable/sysfs-block
> >> still documents the legacy behavior of the io_poll sysfs file. This is
> >> confusing for users trying to figure out reason of the failed or
> >> unexpected behavior after writing to the file and seeing the dmesg,
> >> particularly because there are many articles on the Internet describing
> >> the legacy behavior.
> >> If the maintainers agree, I can help update these documentations.
> >
> > Feel free to update the documentations, AFAIK, there are some out of
> > date descriptions and it's welcome to fix them
>
> Thanks a lot for the information. Before writing anything, I just
> want to confirm there is indeed no more per-device control for
> polling behavior? Is io_uring and driver-specific features like
> nvme passthrough the only ways to go right now?
>
> For users who have legacy applications that could benefit from
> polling but still make traditional IO calls, would it still
> make sense to add a per-device override? I can think of some
> ways of adding a config for a specific device so it would
> tag all bio-s for that device as polling (if queue capable).
> But I'm not sure if that has been discussed before or maybe
> that was intentionally discouraged? Would love to hear from
> the maintainers for opinion.
You can only reach the polling features through io_uring. You can use it
with normal read/write uring commands, or the nvme passthrough uring
commands. Successfully using it requires you have set up your module
parameters to reserve some queues for polling.
The synchronous calls (preadv2/pwritev2) had polling capabilities
removed due to issues. Here's the commit that removed it:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9650b453a3d4b1b8ed4ea8bcb9b40109608d1faf
prev parent reply other threads:[~2025-08-16 3:59 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-14 5:14 Question on setting IO polling behavior and documentations Teng Qin
2025-08-14 9:31 ` Yu Kuai
2025-08-14 22:35 ` Teng Qin
2025-08-16 3:59 ` Keith Busch [this message]
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