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Date:   Wed, 10 Aug 2022 16:49:08 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     io-uring@...r.kernel.org, netdev@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, kernel-team@...com,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        Wei Liu <wei.liu@...nel.org>, Paul Durrant <paul@....org>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: [RFC net-next io_uring 00/11] improve io_uring's ubuf_info refcounting

There is a couple of tricks we can do with io_uring to improve ubuf_info
refcounting. First, we ammortise reference grabbing and then give them
away to the network layer, which is implemented in 8 and 11. Also, we
don't need need additional pinning for TCP, which is removed by 7.

1-4 are needed because otherwise we're out of space in io_notif_data and
using ->desc or some other field of ubuf_info would be ugly. It'll also
facilitate further ideas like adding a simpler notification model for UDP.

liburing/examples/io_uring-sendzc benchmark using a branch containing the
patchset and some more [1] showed ~1.6% qps improvement for UDP (dummy dev),
and ~1% for TCP (localhost + hacks enabling zc).

I didn't specifically test xen and vhost and not sure how, would love
some help with that.

[1] https://github.com/isilence/linux/tree/net/zc-ref-optimisation

Pavel Begunkov (11):
  net: introduce struct ubuf_info_msgzc
  xen/netback: use struct ubuf_info_msgzc
  vhost/net: use struct ubuf_info_msgzc
  net: shrink struct ubuf_info
  net: rename ubuf_info's flags
  net: add flags for controlling ubuf_info
  net/tcp: optimise tcp ubuf refcounting
  net: let callers provide ->msg_ubuf refs
  io_uring/notif: add helper for flushing refs
  io_uring/notif: mark notifs with UARGFL_CALLER_PINNED
  io_uring/notif: add ubuf_info ref caching

 drivers/net/xen-netback/common.h    |  2 +-
 drivers/net/xen-netback/interface.c |  4 +--
 drivers/net/xen-netback/netback.c   |  7 +++---
 drivers/vhost/net.c                 | 17 +++++++------
 include/linux/skbuff.h              | 35 +++++++++++++++++++++++---
 io_uring/net.c                      |  8 +++++-
 io_uring/notif.c                    | 21 ++++++++++------
 io_uring/notif.h                    | 22 +++++++++++++++-
 net/core/skbuff.c                   | 39 ++++++++++++++++-------------
 net/ipv4/ip_output.c                |  3 ++-
 net/ipv4/tcp.c                      | 11 +++++---
 net/ipv6/ip6_output.c               |  3 ++-
 12 files changed, 123 insertions(+), 49 deletions(-)

-- 
2.37.0

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