linux-kernel - Re: [PATCH 0/8] Various io_uring micro-optimizations (reducing lock contention)

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Message-ID: <daaed11f-02c4-4580-9594-fcaef35a35fd@kernel.dk>
Date: Fri, 31 Jan 2025 09:13:58 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Max Kellermann <max.kellermann@...os.com>
Cc: asml.silence@...il.com, io-uring@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/8] Various io_uring micro-optimizations (reducing lock
 contention)

On 1/29/25 11:01 AM, Max Kellermann wrote:
> On Wed, Jan 29, 2025 at 6:45?PM Jens Axboe <axboe@...nel.dk> wrote:
>> Why are you combining it with epoll in the first place? It's a lot more
>> efficient to wait on a/multiple events in io_uring_enter() rather than
>> go back to a serialize one-event-per-notification by using epoll to wait
>> on completions on the io_uring side.
> 
> Yes, I wish I could do that, but that works only if everything is
> io_uring - all or nothing. Most of the code is built around an
> epoll-based loop and will not be ported to io_uring so quickly.
> 
> Maybe what's missing is epoll_wait as io_uring opcode. Then I could
> wrap it the other way. Or am I supposed to use io_uring
> poll_add_multishot for that?

Not a huge fan of adding more epoll logic to io_uring, but you are right
this case may indeed make sense as it allows you to integrate better
that way in existing event loops. I'll take a look.

-- 
Jens Axboe