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

[Michael S. Tsirkin]

On Mon, Apr 04, 2022 at 11:11:16PM +0800, Xianting Tian wrote:
> I can't find it in next branch, will you apply this patch?

yes, thanks!

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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 
---
drivers/virtio/virtio_ring.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)


Reviewed-by: Stefano Garzarella 



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



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

[Jason Wang]

On Mon, Mar 28, 2022 at 6:58 PM Xianting Tian
 wrote:
>
> The 'if (vq->vq.num_free < descs_used)' check will almost always be false.
>
> Signed-off-by: Xianting Tian 

Acked-by: Jason Wang 

> ---
>  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
>

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