IO-Uring Archive on
 help / color / Atom feed
From: Jens Axboe <>
To: Stefano Garzarella <>
Cc: Alexander Viro <>,,,
Subject: Re: [PATCH] io_uring: wakeup threads waiting for EPOLLOUT events
Date: Thu, 16 Jan 2020 09:00:24 -0700
Message-ID: <> (raw)
In-Reply-To: <20200116155557.mwjc7vu33xespiag@steredhat>

On 1/16/20 8:55 AM, Stefano Garzarella wrote:
> On Thu, Jan 16, 2020 at 08:29:07AM -0700, Jens Axboe wrote:
>> On 1/16/20 6:49 AM, Stefano Garzarella wrote:
>>> io_uring_poll() sets EPOLLOUT flag if there is space in the
>>> SQ ring, then we should wakeup threads waiting for EPOLLOUT
>>> events when we expose the new SQ head to the userspace.
>>> Signed-off-by: Stefano Garzarella <>
>>> ---
>>> Do you think is better to change the name of 'cq_wait' and 'cq_fasync'?
>> I honestly think it'd be better to have separate waits for in/out poll,
>> the below patch will introduce some unfortunate cacheline traffic
>> between the submitter and completer side.
> Agree, make sense. I'll send a v2 with a new 'sq_wait'.
> About fasync, do you think could be useful the POLL_OUT support?
> In this case, maybe is not simple to have two separate fasync_struct,
> do you have any advice?

The fasync should not matter, it's all in the checking of whether the sq
side has any sleepers. This is rarely going to be the case, so as long
as we can keep the check cheap, then I think we're fine.

Since the use case is mostly single submitter, unless you're doing
something funky or unusual, you're not going to be needing POLLOUT ever.
Hence I don't want to add any cost for it, I'd even advocate just doing
waitqueue_active() perhaps, if we can safely pull it off.

Jens Axboe

  reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 13:49 Stefano Garzarella
2020-01-16 15:29 ` Jens Axboe
2020-01-16 15:55   ` Stefano Garzarella
2020-01-16 16:00     ` Jens Axboe [this message]
2020-01-16 16:26       ` Stefano Garzarella
2020-01-16 16:30         ` Jens Axboe
2020-01-16 17:03           ` Stefano Garzarella

Reply instructions:

You may reply publically 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:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

IO-Uring Archive on

Archives are clonable:
	git clone --mirror io-uring/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 io-uring io-uring/ \
	public-inbox-index io-uring

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone