Linux Virtualization - Mar 2016 - [net-next v2] virtio_net: replace netdev_alloc_skb_ip_align() with napi_alloc_skb()

This gives small but noticeable rx performance improvement (2-3%)
and will allow exploiting future napi improvement.

Signed-off-by: Paolo Abeni <pabeni at redhat.com>

--
 v2: replace also netdev_alloc_skb_ip_align() invocation in
	add_recvbuf_small(), suggested by Venkatesh Srinivas
---
 drivers/net/virtio_net.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fb0eae4..100e039 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -260,7 +260,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
 	p = page_address(page) + offset;
 
 	/* copy small packet so we can reuse these pages for small data */
-	skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
+	skb = napi_alloc_skb(&rq->napi, GOOD_COPY_LEN);
 	if (unlikely(!skb))
 		return NULL;
 
@@ -541,7 +541,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct
receive_queue *rq,
 	struct virtio_net_hdr_mrg_rxbuf *hdr;
 	int err;
 
-	skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN, gfp);
+	skb = __napi_alloc_skb(&rq->napi, GOOD_PACKET_LEN, gfp);
 	if (unlikely(!skb))
 		return -ENOMEM;
 
-- 
1.8.3.1

On Fri, Mar 18, 2016 at 8:42 AM, Paolo Abeni <pabeni at redhat.com>
wrote:
> This gives small but noticeable rx performance improvement (2-3%)
> and will allow exploiting future napi improvement.
>
> Signed-off-by: Paolo Abeni <pabeni at redhat.com>
>
> --
>  v2: replace also netdev_alloc_skb_ip_align() invocation in
>         add_recvbuf_small(), suggested by Venkatesh Srinivas
> ---
>  drivers/net/virtio_net.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fb0eae4..100e039 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -260,7 +260,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info
*vi,
>         p = page_address(page) + offset;
>
>         /* copy small packet so we can reuse these pages for small data */
> -       skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
> +       skb = napi_alloc_skb(&rq->napi, GOOD_COPY_LEN);
>         if (unlikely(!skb))
>                 return NULL;
>
> @@ -541,7 +541,7 @@ static int add_recvbuf_small(struct virtnet_info *vi,
struct receive_queue *rq,
>         struct virtio_net_hdr_mrg_rxbuf *hdr;
>         int err;
>
> -       skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN,
gfp);
> +       skb = __napi_alloc_skb(&rq->napi, GOOD_PACKET_LEN, gfp);
>         if (unlikely(!skb))
>                 return -ENOMEM;
Sorry, I should've mentioned more in my first reply --
add_recvbuf_small is called from try_fill_recv in both
NAPI and non-NAPI context (NAPI: via virtnet_receive from
virtnet_poll; non-NAPI: via scheduled work,
via virtnet_probe, and via virtnet_restore).

I don't believe you can use __napi_alloc_skb() for the non-NAPI paths,
it'd be a bit more work to plumb
the context as an argument if you think its worth doing here.

Looking forward to bulk skb allocation either way.

HTH,
-- vs;

On Fri, Mar 18, 2016 at 04:42:48PM +0100, Paolo Abeni
wrote:
> This gives small but noticeable rx performance improvement (2-3%)
> and will allow exploiting future napi improvement.
> 
> Signed-off-by: Paolo Abeni <pabeni at redhat.com>
I am not sure this is necessarily worth doing for this dumb hardware.
I queued v1 in vhost tree for now, let's see some performance
numbers before we start changing about other paths.
> --
>  v2: replace also netdev_alloc_skb_ip_align() invocation in
> 	add_recvbuf_small(), suggested by Venkatesh Srinivas
> ---
>  drivers/net/virtio_net.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index fb0eae4..100e039 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -260,7 +260,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info
*vi,
>  	p = page_address(page) + offset;
>  
>  	/* copy small packet so we can reuse these pages for small data */
> -	skb = netdev_alloc_skb_ip_align(vi->dev, GOOD_COPY_LEN);
> +	skb = napi_alloc_skb(&rq->napi, GOOD_COPY_LEN);
>  	if (unlikely(!skb))
>  		return NULL;
>  
> @@ -541,7 +541,7 @@ static int add_recvbuf_small(struct virtnet_info *vi,
struct receive_queue *rq,
>  	struct virtio_net_hdr_mrg_rxbuf *hdr;
>  	int err;
>  
> -	skb = __netdev_alloc_skb_ip_align(vi->dev, GOOD_PACKET_LEN, gfp);
> +	skb = __napi_alloc_skb(&rq->napi, GOOD_PACKET_LEN, gfp);
>  	if (unlikely(!skb))
>  		return -ENOMEM;
>  
> -- 
> 1.8.3.1