Re: [PATCH 2/2] virtio_ring: add unlikely annotation for free descs check

[Stefano Garzarella]

On Mon, Mar 28, 2022 at 06:58:17PM +0800, Xianting Tian wrote:
> The 'if (vq->vq.num_free < descs_used)' check will almost always be false.
>
> Signed-off-by: Xianting Tian <xianting.tian@xxxxxxxxxxxxxxxxx>
> ---
> drivers/virtio/virtio_ring.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>

> 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