[PATCH for-next] io_uring: move finish_wait() outside of loop in cqring_wait()

[Jens Axboe <axboe@kernel.dk>]

We don't need to call this for every loop. This is particularly
troublesome if we are task_work intensive, and get woken more often than
we desire due to that.

Just do it at the end, that's always safe as we initialize the waitqueue
list head anyway. This can save a considerable amount of hammering on
the waitqueue lock, which is also hot from the request completion side.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

---

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 25aafb17d1e2..a83e7a036343 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8359,10 +8359,10 @@ static int io_cqring_wait(struct io_ring_ctx *ctx, int min_events,
 		prepare_to_wait_exclusive(&ctx->cq_wait, &iowq.wq,
 						TASK_INTERRUPTIBLE);
 		ret = io_cqring_wait_schedule(ctx, &iowq, timeout);
-		finish_wait(&ctx->cq_wait, &iowq.wq);
 		cond_resched();
 	} while (ret > 0);
 
+	finish_wait(&ctx->cq_wait, &iowq.wq);
 	restore_saved_sigmask_unless(ret == -EINTR);
 
 	return READ_ONCE(rings->cq.head) == READ_ONCE(rings->cq.tail) ? ret : 0;

-- 
Jens Axboe