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

[Pavel Begunkov <asml.silence@gmail.com>]

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.

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(-)

-- 
2.44.0