[PATCH v6 0/5] io_uring zcrx ifq sharing

[David Wei <dw@davidwei.uk>]

Each ifq is bound to a HW RX queue with no way to share this across
multiple rings. It is possible that one ring will not be able to fully
saturate an entire HW RX queue due to userspace work. There are two ways
to handle more work:

  1. Move work to other threads, but have to pay context switch overhead
     and cold caches.
  2. Add more rings with ifqs, but HW RX queues are a limited resource.

This patchset add a way for multiple rings to share the same underlying
src ifq that is bound to a HW RX queue. Rings with shared ifqs can issue
io_recvzc on zero copy sockets, just like the src ring.

Userspace are expected to create rings in separate threads and not
processes, such that all rings share the same address space. This is
because the sharing and synchronisation of refill rings is purely done
in userspace with no kernel involvement e.g. dst rings do not mmap the
refill ring. Also, userspace must distribute zero copy sockets steered
into the same HW RX queue across rings sharing the ifq.

v6:
 - removed ifq refcounting that merged separately
 - fill in struct io_uring_zcrx_offsets
 - shorten functions + structs
 - move ctx flags checks from export to import

v5:
 - remove sync refill api
 - pp mp taking ref on ifq
 - add ifq export to file
 - implement sharing by importing ifq fd

v4:
 - lock rings in seq instead of both
 - drop export io_lock_two_rings()
 - break circular ref between ifq and ring ctx
 - remove io_shutdown_zcrx_ifqs()
 - copy reg struct to user before writing ifq to ctx->zcrx_ctxs

v3:
 - drop ifq->proxy
 - use dec_and_test to clean up ifq

v2:
 - split patch

David Wei (3):
  io_uring/zcrx: move io_zcrx_scrub() and dependencies up
  io_uring/zcrx: add io_fill_zcrx_offsets()
  io_uring/zcrx: share an ifq between rings

Pavel Begunkov (2):
  io_uring/zcrx: count zcrx users
  io_uring/zcrx: export zcrx via a file

 include/uapi/linux/io_uring.h |   5 +
 io_uring/zcrx.c               | 218 ++++++++++++++++++++++++++--------
 io_uring/zcrx.h               |   2 +
 3 files changed, 173 insertions(+), 52 deletions(-)

-- 
2.47.3