linux-kernel - [PATCH 2/2] virtio_ring: add unlikely annotation for free descs check

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Message-Id: <20220328105817.1028065-2-xianting.tian@linux.alibaba.com>
Date:   Mon, 28 Mar 2022 18:58:17 +0800
From:   Xianting Tian <xianting.tian@...ux.alibaba.com>
To:     mst@...hat.com, jasowang@...hat.com, sgarzare@...hat.com
Cc:     virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Xianting Tian <xianting.tian@...ux.alibaba.com>
Subject: [PATCH 2/2] virtio_ring: add unlikely annotation for free descs check

The 'if (vq->vq.num_free < descs_used)' check will almost always be false.

Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
---
 drivers/virtio/virtio_ring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index d597fc0874ec..ab6d5f0cb579 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -525,7 +525,7 @@ static inline int virtqueue_add_split(struct virtqueue *_vq,
 		descs_used = total_sg;
 	}
 
-	if (vq->vq.num_free < descs_used) {
+	if (unlikely(vq->vq.num_free < descs_used)) {
 		pr_debug("Can't add buf len %i - avail = %i\n",
 			 descs_used, vq->vq.num_free);
 		/* FIXME: for historical reasons, we force a notify here if
-- 
2.17.1