[PATCH for-next 7/7] io_uring: return normal tw run linking optimisation

Pavel Begunkov
2023-01-23T14:42:17Z

io_submit_flush_completions() may produce new task_work items, so it's a
good idea to recheck the task_work list after flushing completions. The
optimisation is not new and was accidentially removed by
f88262e60bb9 ("io_uring: lockless task list")

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
io_uring/io_uring.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 586e70f686ce..8c4d92e64c20 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1238,6 +1238,15 @@ void tctx_task_work(struct callback_head *cb)
loops++;
node = io_llist_xchg(&tctx->task_list, &fake);
count += handle_tw_list(node, &ctx, &uring_locked, &fake);
+
+ /* skip expensive cmpxchg if there are items in the list */
+ if (READ_ONCE(tctx->task_list.first) != &fake)
+ continue;
+ if (uring_locked && !wq_list_empty(&ctx->submit_state.compl_reqs)) {
+ io_submit_flush_completions(ctx);
+ if (READ_ONCE(tctx->task_list.first) != &fake)
+ continue;
+ }
node = io_llist_cmpxchg(&tctx->task_list, &fake, NULL);
} while (node != &fake);

--
2.38.1