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

Commit Message

Pavel Begunkov Jan. 23, 2023, 2:37 p.m. UTC

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 <[e-mail]>
---
 io_uring/io_uring.c | 9 +++++++++
 1 file changed, 9 insertions(+)

Patch

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);