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Message-ID: <673b165c-e971-2dd3-38e5-0cdb1cd3bbac@redhat.com>
Date: Fri, 13 Jan 2023 11:01:35 +0800
From: Jason Wang <jasowang@...hat.com>
To: Heng Qi <hengqi@...ux.alibaba.com>, netdev@...r.kernel.org,
bpf@...r.kernel.org
Cc: "Michael S . Tsirkin" <mst@...hat.com>,
Paolo Abeni <pabeni@...hat.com>,
Jakub Kicinski <kuba@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
"David S . Miller" <davem@...emloft.net>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Eric Dumazet <edumazet@...gle.com>,
Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Subject: Re: [PATCH v3 5/9] virtio-net: construct multi-buffer xdp in
mergeable
在 2023/1/3 14:40, Heng Qi 写道:
> Build multi-buffer xdp using virtnet_build_xdp_buff_mrg().
>
> For the prefilled buffer before xdp is set, we will probably use
> vq reset in the future. At the same time, virtio net currently
> uses comp pages, and bpf_xdp_frags_increase_tail() needs to calculate
> the tailroom of the last frag, which will involve the offset of the
> corresponding page and cause a negative value, so we disable tail
> increase by not setting xdp_rxq->frag_size.
>
> Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
> Reviewed-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Acked-by: Jason Wang <jasowang@...hat.com>
Thanks
> ---
> drivers/net/virtio_net.c | 58 ++++++++++++++++++++++++++++++----------
> 1 file changed, 44 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 699e376b8f8b..ab01cf3855bc 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1036,7 +1036,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> unsigned int metasize = 0;
> unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> - unsigned int frame_sz;
> + unsigned int frame_sz, xdp_room;
> int err;
>
> head_skb = NULL;
> @@ -1057,11 +1057,14 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> rcu_read_lock();
> xdp_prog = rcu_dereference(rq->xdp_prog);
> if (xdp_prog) {
> + unsigned int xdp_frags_truesz = 0;
> + struct skb_shared_info *shinfo;
> struct xdp_frame *xdpf;
> struct page *xdp_page;
> struct xdp_buff xdp;
> void *data;
> u32 act;
> + int i;
>
> /* Transient failure which in theory could occur if
> * in-flight packets from before XDP was enabled reach
> @@ -1077,14 +1080,16 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> */
> frame_sz = truesize;
>
> - /* This happens when rx buffer size is underestimated
> - * or headroom is not enough because of the buffer
> - * was refilled before XDP is set. This should only
> - * happen for the first several packets, so we don't
> - * care much about its performance.
> + /* This happens when headroom is not enough because
> + * of the buffer was prefilled before XDP is set.
> + * This should only happen for the first several packets.
> + * In fact, vq reset can be used here to help us clean up
> + * the prefilled buffers, but many existing devices do not
> + * support it, and we don't want to bother users who are
> + * using xdp normally.
> */
> - if (unlikely(num_buf > 1 ||
> - headroom < virtnet_get_headroom(vi))) {
> + if (!xdp_prog->aux->xdp_has_frags &&
> + (num_buf > 1 || headroom < virtnet_get_headroom(vi))) {
> /* linearize data for XDP */
> xdp_page = xdp_linearize_page(rq, &num_buf,
> page, offset,
> @@ -1095,17 +1100,29 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> if (!xdp_page)
> goto err_xdp;
> offset = VIRTIO_XDP_HEADROOM;
> + } else if (unlikely(headroom < virtnet_get_headroom(vi))) {
> + xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
> + sizeof(struct skb_shared_info));
> + if (len + xdp_room > PAGE_SIZE)
> + goto err_xdp;
> +
> + xdp_page = alloc_page(GFP_ATOMIC);
> + if (!xdp_page)
> + goto err_xdp;
> +
> + memcpy(page_address(xdp_page) + VIRTIO_XDP_HEADROOM,
> + page_address(page) + offset, len);
> + frame_sz = PAGE_SIZE;
> + offset = VIRTIO_XDP_HEADROOM;
> } else {
> xdp_page = page;
> }
>
> - /* Allow consuming headroom but reserve enough space to push
> - * the descriptor on if we get an XDP_TX return code.
> - */
> data = page_address(xdp_page) + offset;
> - xdp_init_buff(&xdp, frame_sz - vi->hdr_len, &rq->xdp_rxq);
> - xdp_prepare_buff(&xdp, data - VIRTIO_XDP_HEADROOM + vi->hdr_len,
> - VIRTIO_XDP_HEADROOM, len - vi->hdr_len, true);
> + err = virtnet_build_xdp_buff_mrg(dev, vi, rq, &xdp, data, len, frame_sz,
> + &num_buf, &xdp_frags_truesz, stats);
> + if (unlikely(err))
> + goto err_xdp_frags;
>
> act = bpf_prog_run_xdp(xdp_prog, &xdp);
> stats->xdp_packets++;
> @@ -1201,6 +1218,19 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> __free_pages(xdp_page, 0);
> goto err_xdp;
> }
> +err_xdp_frags:
> + if (unlikely(xdp_page != page))
> + __free_pages(xdp_page, 0);
> +
> + if (xdp_buff_has_frags(&xdp)) {
> + shinfo = xdp_get_shared_info_from_buff(&xdp);
> + for (i = 0; i < shinfo->nr_frags; i++) {
> + xdp_page = skb_frag_page(&shinfo->frags[i]);
> + put_page(xdp_page);
> + }
> + }
> +
> + goto err_xdp;
> }
> rcu_read_unlock();
>
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