[PATCH for-next 0/7] io_uring: defer task work to when it is needed

[Dylan Yudaken <dylany@fb.com>]

We have seen workloads which suffer due to the way task work is currently
scheduled. This scheduling can cause non-trivial tasks to run interrupting
useful work on the workload. For example in network servers, a large async
recv may run, calling memcpy on a large packet, interrupting a send. Which
would add latency.

This series adds an option to defer async work until user space calls
io_uring_enter with the GETEVENTS flag. This allows the workload to choose
when to schedule async work and have finer control (at the expense of
complexity of managing this) of scheduling.

Patches 1/2/3 are prep patches
Patch 4 changes io_uring_enter to not always pre-run task work. It is not
obvious that this is useful regardless of this series
Patch 5/6/7 adds the new flag and functionality

Dylan Yudaken (7):
  io_uring: use local ctx variable
  io_uring: remove unnecessary variable
  io_uring: introduce io_has_work
  io_uring: do not always run task work at the start of io_uring_enter
  io_uring: add IORING_SETUP_DEFER_TASKRUN
  io_uring: move io_eventfd_put
  io_uring: signal registered eventfd to process deferred task work

 include/linux/io_uring_types.h |   3 +
 include/uapi/linux/io_uring.h  |   7 +
 io_uring/cancel.c              |   2 +-
 io_uring/io_uring.c            | 232 +++++++++++++++++++++++++--------
 io_uring/io_uring.h            |  31 ++++-
 io_uring/rsrc.c                |   2 +-
 6 files changed, 221 insertions(+), 56 deletions(-)


base-commit: ff34d8d06a1f16b6a58fb41bfbaa475cc6c02497
-- 
2.30.2