netdev - Re: [PATCH next-next-2.6 v2] virtio_net: missing sg_init

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Date:	Wed, 31 Mar 2010 12:20:22 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	David Miller <davem@...emloft.net>,
	Thomas Müller <thomas@...htm.de>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH next-next-2.6 v2] virtio_net: missing sg_init_table

On Mon, Mar 29, 2010 at 06:19:15PM -0700, Shirley Ma wrote:
> Add missing sg_init_table for sg_set_buf in virtio_net which
> induced in defer skb patch.
> 
> Reported-by: Thomas Müller <thomas@...htm.de>
> Tested-by: Thomas Müller <thomas@...htm.de>
> Signed-off-by: Shirley Ma <xma@...ibm.com>

I'm concerned that the 'big' path might cause a performance regression.
Let's move sg into virtnet_info so that this needs to be only called
once?

> ---
>  drivers/net/virtio_net.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 25dc77c..3f5be35 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -326,6 +326,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, gfp_t gfp)
>  	struct scatterlist sg[2];
>  	int err;
>  
> +	sg_init_table(sg, 2);
>  	skb = netdev_alloc_skb_ip_align(vi->dev, MAX_PACKET_LEN);
>  	if (unlikely(!skb))
>  		return -ENOMEM;
> @@ -351,6 +352,7 @@ static int add_recvbuf_big(struct virtnet_info *vi, gfp_t gfp)
>  	char *p;
>  	int i, err, offset;
>  
> +	sg_init_table(sg, MAX_SKB_FRAGS + 2);
>  	/* page in sg[MAX_SKB_FRAGS + 1] is list tail */
>  	for (i = MAX_SKB_FRAGS + 1; i > 1; --i) {
>  		first = get_a_page(vi, gfp);
> 
> 
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