Re: [RFC 0/6] implement io_uring notification (ubuf_info) stacking

[David Ahern <dsahern@kernel.org>]

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 ubuf_info forces TCP segmentation at less than MTU boundaries which
kills performance with small message sizes as TCP is forced to send
small packets. This is an interesting solution to allow the byte stream
to flow yet maintain the segmentation boundaries for callbacks.

> 
> 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.
> 
> Testing with liburing/examples/send-zerocopy and another custom made
> tool, with 4K bytes per send it improves performance ~6 times and
> levels it with MSG_ZEROCOPY. Without the patchset it requires much
> larger sends to utilise all potential.
> 
> bytes  | before | after (Kqps)  
> 100    | 283    | 936
> 1200   | 195    | 1023
> 4000   | 193    | 1386
> 8000   | 154    | 1058
> 
> Pavel Begunkov (6):
>   net: extend ubuf_info callback to ops structure
>   net: add callback for setting a ubuf_info to skb
>   io_uring/notif: refactor io_tx_ubuf_complete()
>   io_uring/notif: remove ctx var from io_notif_tw_complete
>   io_uring/notif: simplify io_notif_flush()
>   io_uring/notif: implement notification stacking
> 
>  drivers/net/tap.c      |  2 +-
>  drivers/net/tun.c      |  2 +-
>  drivers/vhost/net.c    |  8 +++-
>  include/linux/skbuff.h | 21 ++++++----
>  io_uring/notif.c       | 91 +++++++++++++++++++++++++++++++++++-------
>  io_uring/notif.h       | 13 +++---
>  net/core/skbuff.c      | 37 +++++++++++------
>  7 files changed, 129 insertions(+), 45 deletions(-)
>