[PATCHSET for-next 0/6] task work cleanups

[Jens Axboe <axboe@kernel.dk>]

Hi,

This patchset gets rid of using llist for handling task_work, for both
local and normal task_work. Instead of a lockless list, a normal
io_wq_work_list is used and protected by a spinlock. I've done some
benchmarking with this, and I only see wins with this - the act of
adding or iterating task_work is the same cost, but we get rid of the
need to reverse the task_work list, which can be substantial for bursty
applications or just generally busy task_work usages.

Patch 2 implements io_wq_work_list handling for deferred task_work, and
patch 4 does the same for normal task_work. Patch 6 then also switches
SQPOLL to use this scheme, which eliminates the passing around of
io_wq_work_node for its retry logic.

Outside of cleaning up this code, it also enables us to potentially
implement task_work run capping for normal task_work in the future.

Git tree can be found here:

https://git.kernel.dk/cgit/linux/log/?h=io_uring-defer-tw

 include/linux/io_uring_types.h |  17 +-
 io_uring/io_uring.c            | 293 ++++++++++++++++++---------------
 io_uring/io_uring.h            |  20 ++-
 io_uring/slist.h               |  16 ++
 io_uring/sqpoll.c              |  20 ++-
 io_uring/tctx.c                |   3 +-
 6 files changed, 211 insertions(+), 158 deletions(-)

-- 
Jens Axboe