netdev - Re: [net-next v2] virtio_net: replace netdev_alloc_skb_ip_align() with napi_alloc

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Date:	Sun, 20 Mar 2016 14:28:23 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Paolo Abeni <pabeni@...hat.com>
Cc:	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Venkatesh Srinivas <venkateshs@...gle.com>
Subject: Re: [net-next v2] virtio_net: replace netdev_alloc_skb_ip_align()
 with napi_alloc_skb()

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@...hat.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