linux-kernel - Re: [RFC PATCH net-next v2 1/2] virtio-net: support zerocopy multi buffer XDP in mergeable

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Message-ID: <d855c95e-06db-4c68-af01-8997ce9b9257@oracle.com>
Date: Wed, 28 May 2025 22:14:26 +0530
From: ALOK TIWARI <alok.a.tiwari@...cle.com>
To: Bui Quang Minh <minhquangbui99@...il.com>, netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Eugenio Pérez
 <eperezma@...hat.com>,
        Andrew Lunn <andrew+netdev@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [RFC PATCH net-next v2 1/2] virtio-net: support zerocopy multi
 buffer XDP in mergeable



On 27-05-2025 21:49, Bui Quang Minh wrote:
> Currently, in zerocopy mode with mergeable receive buffer, virtio-net
> does not support multi buffer but a single buffer only. This commit adds
> support for multi mergeable receive buffer in the zerocopy XDP path by
> utilizing XDP buffer with frags.
> 
> Signed-off-by: Bui Quang Minh <minhquangbui99@...il.com>
> ---
>   drivers/net/virtio_net.c | 123 +++++++++++++++++++++------------------
>   1 file changed, 66 insertions(+), 57 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e53ba600605a..a9558650f205 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -45,6 +45,8 @@ module_param(napi_tx, bool, 0644);
>   #define VIRTIO_XDP_TX		BIT(0)
>   #define VIRTIO_XDP_REDIR	BIT(1)
>   
> +#define VIRTNET_MAX_ZC_SEGS	8
> +
>   /* RX packet size EWMA. The average packet size is used to determine the packet
>    * buffer size when refilling RX rings. As the entire RX ring may be refilled
>    * at once, the weight is chosen so that the EWMA will be insensitive to short-
> @@ -1232,65 +1234,53 @@ static void xsk_drop_follow_bufs(struct net_device *dev,
>   	}
>   }
>   
> -static int xsk_append_merge_buffer(struct virtnet_info *vi,
> -				   struct receive_queue *rq,
> -				   struct sk_buff *head_skb,
> -				   u32 num_buf,
> -				   struct virtio_net_hdr_mrg_rxbuf *hdr,
> -				   struct virtnet_rq_stats *stats)
> +static int virtnet_build_xsk_buff_mrg(struct virtnet_info *vi,
> +				      struct receive_queue *rq,
> +				      u32 num_buf,
> +				      struct xdp_buff *xdp,
> +				      struct virtnet_rq_stats *stats)
>   {
> -	struct sk_buff *curr_skb;
> -	struct xdp_buff *xdp;
> -	u32 len, truesize;
> -	struct page *page;
> +	unsigned int len;
>   	void *buf;
>   
> -	curr_skb = head_skb;
> +	if (num_buf < 2)
> +		return 0;
> +
> +	while (num_buf > 1) {
> +		struct xdp_buff *new_xdp;
>   
> -	while (--num_buf) {
>   		buf = virtqueue_get_buf(rq->vq, &len);
> -		if (unlikely(!buf)) {
> -			pr_debug("%s: rx error: %d buffers out of %d missing\n",
> -				 vi->dev->name, num_buf,
> -				 virtio16_to_cpu(vi->vdev,
> -						 hdr->num_buffers));
> +		if (!unlikely(buf)) {

if (unlikely(!buf)) { ?

> +			pr_debug("%s: rx error: %d buffers missing\n",
> +				 vi->dev->name, num_buf);
>   			DEV_STATS_INC(vi->dev, rx_length_errors);

Thanks,
Alok