io_uring: optimise rw comletion handlers

Don't override req->result in io_complete_rw_iopoll() when it's already
of the same value, we have an if just above it, so move the assignment
there. Also, add one simle unlikely() in __io_complete_rw_common().
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8dfeb4f84026a20172bcf82c05010abe955874ae.1634144845.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -2640,7 +2640,7 @@ static bool __io_complete_rw_common(struct io_kiocb *req, long res)
 {
 	if (req->rw.kiocb.ki_flags & IOCB_WRITE)
 		kiocb_end_write(req);
-	if (res != req->result) {
+	if (unlikely(res != req->result)) {
 		if ((res == -EAGAIN || res == -EOPNOTSUPP) &&
 		    io_rw_should_reissue(req)) {
 			req->flags |= REQ_F_REISSUE;
@@ -2695,9 +2695,9 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb, long res, long res2)
 			req->flags |= REQ_F_REISSUE;
 			return;
 		}
+		req->result = res;
 	}
 
-	req->result = res;
 	/* order with io_iopoll_complete() checking ->iopoll_completed */
 	smp_store_release(&req->iopoll_completed, 1);
 }