netdev - Re: [RFC 0/6] implement io_uring notification (ubuf

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Message-ID: <b44684a5-13b4-4717-a653-cfd0c920bb49@kernel.dk>
Date: Fri, 12 Apr 2024 07:44:36 -0600
From: Jens Axboe <axboe@...nel.dk>
To: Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
 netdev@...r.kernel.org
Cc: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski
 <kuba@...nel.org>, David Ahern <dsahern@...nel.org>,
 Eric Dumazet <edumazet@...gle.com>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [RFC 0/6] implement io_uring notification (ubuf_info) stacking

On 4/12/24 6:55 AM, Pavel Begunkov wrote:
> io_uring allocates a ubuf_info per zerocopy send request, it's convenient
> for the userspace but with how things are it means that every time the 
> TCP stack has to allocate a new skb instead of amending into a previous
> one. Unless sends are big enough, there will be lots of small skbs
> straining the stack and dipping performance.
> 
> The patchset implements notification, i.e. an io_uring's ubuf_info
> extension, stacking. It tries to link ubuf_info's into a list, and
> the entire link will be put down together once all references are
> gone.

Excellent! I'll take a closer look, but I ran a quick test with my test
tool just to see the difference. This is on a 100G link.

Packet size	Before (Mbit)    After (Mbit)   Diff
====================================================
100		290		  1250		4.3x
200		560		  2460		4.4x
400		1190		  4900		4.1x
800		2300		  9700		4.2x
1600		4500		 19100		4.2x
3200		8900		 35000		3.9x

which are just rough numbers and the tool isn't that great, but
definitely encouraging. And it does have parity with sync MSG_ZEROPCY,
which is what I was really bugged about before.

-- 
Jens Axboe