Re: Emulating epoll

[Jesse Hughes <jesse@eqalpha.com>]

Awesome, thanks for the info and your hard work Pavel!

Cheers,
Jesse

________________________________________
From: Pavel Begunkov <asml.silence@gmail.com>
Sent: Tuesday, April 20, 2021 9:59 AM
To: Jesse Hughes; io-uring@vger.kernel.org
Cc: John
Subject: Re: Emulating epoll

On 4/20/21 5:37 PM, Jesse Hughes wrote:
> Hello,
>
> I want to start by saying thank-you for working on io_uring.  My experience using it thus far has been great.
>
> I'm working on an open-source database product (KeyDB, a multi-threaded redis fork) and we're considering rewriting our IO to use io_uring.  Our current implementation uses epoll, and processes IO on (mainly) sockets as they become ready.

Wonderful, always interesting to learn about emerging use cases
and new apps using it.

>
> If I'm understanding the literature correctly, to emulate epoll, we should be able to set up a uring, put in a read sqe for each incoming socket connection, then (using liburing) call io_uring_wait_sqe​.  Correct?  Is there a better way of doing that?

In general, the best way to do I/O is to issue a read/write/etc. sqe
directly as you've mentioned. io_uring will take care of doing polling
internally or finding a better way to execute it.

However, to simply emulate epoll IORING_OP_POLL_ADD requests can be
used There is support for multi-shot poll requests, which Jens added
for coming linux 5.13

>
> Our end-goal is not to emulate epoll, but that seems like the quickest way of getting something working that we can do further experiments with.
>
> For reference, if anyone's interested, our source repo is at : https://github.com/EQ-Alpha/KeyDB

--
Pavel Begunkov