[RFC 00/11] aio: add the aio_add_sqe() io_uring API

[Stefan Hajnoczi <stefanha@redhat.com>]

This patch series contains io_uring improvements:

1. Support the glib event loop in fdmon-io_uring.
   - aio-posix: fix polling mode with fdmon-io_uring
   - aio-posix: keep polling enabled with fdmon-io_uring.c
   - tests/unit: skip test-nested-aio-poll with io_uring
   - aio-posix: integrate fdmon into glib event loop

2. Enable fdmon-io_uring on hosts where io_uring is available at runtime.
   Otherwise continue using ppoll(2) or epoll(7).
   - aio: remove aio_context_use_g_source()

3. Add the new aio_add_sqe() API for submitting io_uring requests in the QEMU
   event loop.
   - aio: free AioContext when aio_context_new() fails
   - aio: add errp argument to aio_context_setup()
   - aio-posix: gracefully handle io_uring_queue_init() failure
   - aio-posix: add aio_add_sqe() API for user-defined io_uring requests
   - aio-posix: avoid EventNotifier for cqe_handler_bh

4. Use aio_add_sqe() in block/io_uring.c instead of creating a dedicated
   io_uring context for --blockdev aio=io_uring. This simplifies the code,
   reduces the number of file descriptors, and demonstrates the aio_add_sqe()
   API.
   - block/io_uring: use aio_add_sqe()

The highlight is aio_add_sqe(), which is needed for the FUSE-over-io_uring
Google Summer of Code project and other future QEMU features that natively use
Linux io_uring functionality.

I'm not happy with performance yet. This is why I've marked the series as
Request For Comments:
rw        bs iodepth aio    iothread before after  diff
randread  4k       1 native        0  76281 79707  +4.5%
randread  4k      64 native        0 255078 247293 -3.1%
randwrite 4k       1 native        0 132706 123337 -7.1%
randwrite 4k      64 native        0 275589 245192 -11%
randread  4k       1 io_uring      0  75284 78023  +3.5%
randread  4k      64 io_uring      0 254637 248222 -2.5%
randwrite 4k       1 io_uring      0 126519 128641 +1.7%
randwrite 4k      64 io_uring      0 258967 249266 -3.7%
randread  4k       1 native        1  90557 88436  -2.3%
randread  4k      64 native        1 290673 280456 -3.5%
randwrite 4k       1 native        1 183015 169106 -7.6%
randwrite 4k      64 native        1 281316 280078 -0.4%
randread  4k       1 io_uring      1  92479 86983  -5.9%
randread  4k      64 io_uring      1 304229 257730 -15.3%
randwrite 4k       1 io_uring      1 183983 157425 -14.4%
randwrite 4k      64 io_uring      1 299979 264156 -11.9%

Overall the performance decreases, so I need to continue profiling the
iodepth=64 cases with aio=native and aio=io_uring.

This series replaces the following older series that were held off from merging
until the QEMU 10.1 development window opened and the performance results were
collected:
- "[PATCH 0/3] [RESEND] block: unify block and fdmon io_uring"
- "[PATCH 0/4] aio-posix: integrate fdmon into glib event loop"

Stefan Hajnoczi (11):
  aio-posix: fix polling mode with fdmon-io_uring
  aio-posix: keep polling enabled with fdmon-io_uring.c
  tests/unit: skip test-nested-aio-poll with io_uring
  aio-posix: integrate fdmon into glib event loop
  aio: remove aio_context_use_g_source()
  aio: free AioContext when aio_context_new() fails
  aio: add errp argument to aio_context_setup()
  aio-posix: gracefully handle io_uring_queue_init() failure
  aio-posix: add aio_add_sqe() API for user-defined io_uring requests
  aio-posix: avoid EventNotifier for cqe_handler_bh
  block/io_uring: use aio_add_sqe()

 meson.build                       |   2 +-
 include/block/aio.h               | 134 +++++++-
 include/block/raw-aio.h           |   5 -
 util/aio-posix.h                  |  18 +-
 block/file-posix.c                |  38 +--
 block/io_uring.c                  | 489 +++++++-----------------------
 stubs/io_uring.c                  |  32 --
 tests/unit/test-aio.c             |   7 +-
 tests/unit/test-nested-aio-poll.c |  13 +-
 util/aio-posix.c                  | 134 ++++----
 util/aio-win32.c                  |   6 +-
 util/async.c                      |  53 +---
 util/fdmon-epoll.c                |  52 +++-
 util/fdmon-io_uring.c             | 218 ++++++++++---
 util/fdmon-poll.c                 |  88 +++++-
 block/trace-events                |  12 +-
 stubs/meson.build                 |   3 -
 util/trace-events                 |   4 +
 18 files changed, 668 insertions(+), 640 deletions(-)
 delete mode 100644 stubs/io_uring.c

-- 
2.49.0