Re: [PATCH net-next v3 5/8] virtio-net: xsk zero copy xmit support xsk unaligned mode

[Jason Wang <jasowang@redhat.com>]

在 2021/3/31 下午3:11, Xuan Zhuo 写道:
> In xsk unaligned mode, the frame pointed to by desc may span two
> consecutive pages, but not more than two pages.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Reviewed-by: Dust Li <dust.li@linux.alibaba.com>


I'd squash this patch into patch 4.


> ---
>   drivers/net/virtio_net.c | 30 ++++++++++++++++++++++++------
>   1 file changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c8a317a93ef7..259fafcf6028 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -2562,24 +2562,42 @@ static void virtnet_xsk_check_space(struct send_queue *sq)
>   static int virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
>   			    struct xdp_desc *desc)
>   {
> +	u32 offset, n, i, copy, copied;


Let's use a better name since we don't actually copy anything here.


>   	struct virtnet_info *vi;
>   	struct page *page;
>   	void *data;
> -	u32 offset;
> +	int err, m;
>   	u64 addr;
> -	int err;
>   
>   	vi = sq->vq->vdev->priv;
>   	addr = desc->addr;
> +
>   	data = xsk_buff_raw_get_data(pool, addr);
> +
>   	offset = offset_in_page(data);
> +	m = desc->len - (PAGE_SIZE - offset);
> +	/* xsk unaligned mode, desc will use two page */
> +	if (m > 0)
> +		n = 3;
> +	else
> +		n = 2;
>   
> -	sg_init_table(sq->sg, 2);
> +	sg_init_table(sq->sg, n);
>   	sg_set_buf(sq->sg, &xsk_hdr, vi->hdr_len);
> -	page = xsk_buff_xdp_get_page(pool, addr);
> -	sg_set_page(sq->sg + 1, page, desc->len, offset);
>   
> -	err = virtqueue_add_outbuf(sq->vq, sq->sg, 2, NULL, GFP_ATOMIC);
> +	copied = 0;
> +	for (i = 1; i < n; ++i) {
> +		copy = min_t(int, desc->len - copied, PAGE_SIZE - offset);
> +
> +		page = xsk_buff_xdp_get_page(pool, addr + copied);
> +
> +		sg_set_page(sq->sg + i, page, copy, offset);
> +		copied += copy;
> +		if (offset)
> +			offset = 0;
> +	}


Can we simplify the codes by using while here? Then I think we don't 
need to determine the value of n.

Thanks


> +
> +	err = virtqueue_add_outbuf(sq->vq, sq->sg, n, NULL, GFP_ATOMIC);
>   	if (unlikely(err))
>   		sq->xsk.last_desc = *desc;
>