This is a note to let you know that I've just added the patch titled
io_uring: adjust defer tw counting
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
io_uring-adjust-defer-tw-counting.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 5f79c202aba81ca8c13c828fdea51a268de33de8
Author: Pavel Begunkov <asml.silence@xxxxxxxxx>
Date: Wed Jan 17 00:57:26 2024 +0000
io_uring: adjust defer tw counting
[ Upstream commit dc12d1799ce710fd90abbe0ced71e7e1ae0894fc ]
The UINT_MAX work item counting bias in io_req_local_work_add() in case
of !IOU_F_TWQ_LAZY_WAKE works in a sense that we will not miss a wake up,
however it's still eerie. In particular, if we add a lazy work item
after a non-lazy one, we'll increment it and get nr_tw==0, and
subsequent adds may try to unnecessarily wake up the task, which is
though not so likely to happen in real workloads.
Half the bias, it's still large enough to be larger than any valid
->cq_wait_nr, which is limited by IORING_MAX_CQ_ENTRIES, but further
have a good enough of space before it overflows.
Fixes: 8751d15426a31 ("io_uring: reduce scheduling due to tw")
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
Link: https://lore.kernel.org/r/108b971e958deaf7048342930c341ba90f75d806.1705438669.git.asml.silence@xxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 1cc4c7b05949..ea772a02c140 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1339,7 +1339,7 @@ static inline void io_req_local_work_add(struct io_kiocb *req, unsigned flags)
nr_tw = nr_tw_prev + 1;
/* Large enough to fail the nr_wait comparison below */
if (!(flags & IOU_F_TWQ_LAZY_WAKE))
- nr_tw = -1U;
+ nr_tw = INT_MAX;
req->nr_tw = nr_tw;
req->io_task_work.node.next = first;
