src/queue: only enter the kernel if both submit and need_enter are true

We just take the submit count, and then unconditionally just call sq_ring_needs_enter() to ensure that flags are set appropriately. Only set need_enter for the submit side if sq_ring_needs_enter() is true, which may not be the case if SQPOLL is used. This can avoid a system call if we're not waiting on any CQEs, and the thread is already running. Reported-by: Olivier Langlois <[email protected]> Link: #429 (comment) Signed-off-by: Jens Axboe <[email protected]>
axboe · Sep 23, 2021 · ca9252f · ca9252f
1 parent 7faebb8
commit ca9252f
Showing 1 changed file with 1 addition and 3 deletions.
diff --git a/src/queue.c b/src/queue.c
@@ -112,10 +112,8 @@ static int _io_uring_get_cqe(struct io_uring *ring, struct io_uring_cqe **cqe_pt
 			flags = IORING_ENTER_GETEVENTS | data->get_flags;
 			need_enter = true;
 		}
-		if (data->submit) {
-			sq_ring_needs_enter(ring, &flags);
+		if (data->submit && sq_ring_needs_enter(ring, &flags))
 			need_enter = true;
-		}
 		if (!need_enter)
 			break;