From: Jens Axboe <[email protected]>
To: Victor Stewart <[email protected]>, io-uring <[email protected]>
Subject: Re: io_uring_prep_timeout_update on linked timeouts
Date: Fri, 27 Aug 2021 21:22:25 -0600 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <CAM1kxwiAF3tmF8PxVf6KPV+Qsg_180sFvebxos5ySmU=TqxgmA@mail.gmail.com>
On 8/26/21 7:40 PM, Victor Stewart wrote:
> On Wed, Aug 25, 2021 at 2:27 AM Victor Stewart <[email protected]> wrote:
>>
>> On Tue, Aug 24, 2021 at 11:43 PM Victor Stewart <[email protected]> wrote:
>>>
>>> we're able to update timeouts with io_uring_prep_timeout_update
>>> without having to cancel
>>> and resubmit, has it ever been considered adding this ability to
>>> linked timeouts?
>>
>> whoops turns out this does work. just tested it.
>
> doesn't work actually. missed that because of a bit of misdirection.
> returns -ENOENT.
>
> the problem with the current way of cancelling then resubmitting
> a new a timeout linked op (let's use poll here) is you have 3 situations:
>
> 1) the poll triggers and you get some positive value. all good.
>
> 2) the linked timeout triggers and cancels the poll, so the poll
> operation returns -ECANCELED.
>
> 3) you cancel the existing poll op, and submit a new one with
> the updated linked timeout. now the original poll op returns
> -ECANCELED.
>
> so solely from looking at the return value of the poll op in 2) and 3)
> there is no way to disambiguate them. of course the linked timeout
> operation result will allow you to do so, but you'd have to persist state
> across cqe processings. you can also track the cancellations and know
> to skip the explicitly cancelled ops' cqes (which is what i chose).
>
> there's also the problem of efficiency. you can imagine in a QUIC
> server where you're constantly updating that poll timeout in response
> to idle timeout and ACK scheduling, this extra work mounts.
>
> so i think the ability to update linked timeouts via
> io_uring_prep_timeout_update would be fantastic.
Hmm, I'll need to dig a bit, but whether it's a linked timeout or not
should not matter. It's a timeout, it's queued and updated the same way.
And we even check this in some of the liburing tests.
Do you have a test case that doesn't work for you? Always easier to
reason about a test case.
--
Jens Axboe
next prev parent reply other threads:[~2021-08-28 3:22 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 22:43 io_uring_prep_timeout_update on linked timeouts Victor Stewart
2021-08-25 1:27 ` Victor Stewart
2021-08-27 1:40 ` Victor Stewart
2021-08-28 3:22 ` Jens Axboe [this message]
2021-08-28 13:39 ` Pavel Begunkov
2021-08-28 13:43 ` Jens Axboe
2021-08-28 21:38 ` Pavel Begunkov
2021-08-29 2:40 ` Jens Axboe
2021-08-31 11:36 ` Victor Stewart
2021-08-31 16:09 ` Pavel Begunkov
2021-08-31 16:07 ` Pavel Begunkov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox