[PATCH v2 for-next 0/8] io_uring: tw contention improvments

[Dylan Yudaken <dylany@fb.com>]

Task work currently uses a spin lock to guard task_list and
task_running. Some use cases such as networking can trigger task_work_add
from multiple threads all at once, which suffers from contention here.

This can be changed to use a lockless list which seems to have better
performance. Running the micro benchmark in [1] I see 20% improvment in
multithreaded task work add. It required removing the priority tw list
optimisation, however it isn't clear how important that optimisation is.
Additionally it has fairly easy to break semantics.

Patch 1-2 remove the priority tw list optimisation
Patch 3-5 add lockless lists for task work
Patch 6 fixes a bug I noticed in io_uring event tracing
Patch 7-8 adds tracing for task_work_run

v2 changes:
 - simplify comparison in handle_tw_list

Dylan Yudaken (8):
  io_uring: remove priority tw list optimisation
  io_uring: remove __io_req_task_work_add
  io_uring: lockless task list
  io_uring: introduce llist helpers
  io_uring: batch task_work
  io_uring: move io_uring_get_opcode out of TP_printk
  io_uring: add trace event for running task work
  io_uring: trace task_work_run

 include/linux/io_uring_types.h  |   2 +-
 include/trace/events/io_uring.h |  72 +++++++++++++--
 io_uring/io_uring.c             | 149 ++++++++++++--------------------
 io_uring/io_uring.h             |   1 -
 io_uring/rw.c                   |   2 +-
 io_uring/tctx.c                 |   4 +-
 io_uring/tctx.h                 |   7 +-
 7 files changed, 126 insertions(+), 111 deletions(-)


base-commit: 7b411672f03db4aa05dec1c96742fc02b99de3d4
-- 
2.30.2