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Date: Fri, 2 Mar 2018 19:36:14 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, brouer@...hat.com,
john.fastabend@...il.com
Subject: Re: [PATCH net V2] virtio-net: re enable XDP_REDIRECT for mergeable
buffer
On Fri, Mar 02, 2018 at 05:29:14PM +0800, Jason Wang wrote:
> XDP_REDIRECT support for mergeable buffer was removed since commit
> 7324f5399b06 ("virtio_net: disable XDP_REDIRECT in receive_mergeable()
> case"). This is because we don't reserve enough tailroom for struct
> skb_shared_info which breaks XDP assumption. So this patch fixes this
> by reserving enough tailroom and using fixed size of rx buffer.
>
> Signed-off-by: Jason Wang <jasowang@...hat.com>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
I think the next incremental step is to look at splitting
out fast path XDP processing to a separate set of functions.
> ---
> Changes from V1:
> - do not add duplicated tracepoint when redirection fails
> ---
> drivers/net/virtio_net.c | 54 +++++++++++++++++++++++++++++++++++++-----------
> 1 file changed, 42 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 9bb9e56..426dcf7 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -504,6 +504,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> page_off += *len;
>
> while (--*num_buf) {
> + int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> unsigned int buflen;
> void *buf;
> int off;
> @@ -518,7 +519,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> /* guard against a misconfigured or uncooperative backend that
> * is sending packet larger than the MTU.
> */
> - if ((page_off + buflen) > PAGE_SIZE) {
> + if ((page_off + buflen + tailroom) > PAGE_SIZE) {
> put_page(p);
> goto err_buf;
> }
> @@ -690,6 +691,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> unsigned int truesize;
> unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> bool sent;
> + int err;
>
> head_skb = NULL;
>
> @@ -701,7 +703,12 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> void *data;
> u32 act;
>
> - /* This happens when rx buffer size is underestimated */
> + /* 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.
> + */
> if (unlikely(num_buf > 1 ||
> headroom < virtnet_get_headroom(vi))) {
> /* linearize data for XDP */
> @@ -736,9 +743,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>
> act = bpf_prog_run_xdp(xdp_prog, &xdp);
>
> - if (act != XDP_PASS)
> - ewma_pkt_len_add(&rq->mrg_avg_pkt_len, len);
> -
> switch (act) {
> case XDP_PASS:
> /* recalculate offset to account for any header
> @@ -770,6 +774,18 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> goto err_xdp;
> rcu_read_unlock();
> goto xdp_xmit;
> + case XDP_REDIRECT:
> + err = xdp_do_redirect(dev, &xdp, xdp_prog);
> + if (err) {
> + if (unlikely(xdp_page != page))
> + put_page(xdp_page);
> + goto err_xdp;
> + }
> + *xdp_xmit = true;
> + if (unlikely(xdp_page != page))
> + goto err_xdp;
> + rcu_read_unlock();
> + goto xdp_xmit;
> default:
> bpf_warn_invalid_xdp_action(act);
> case XDP_ABORTED:
> @@ -1013,13 +1029,18 @@ static int add_recvbuf_big(struct virtnet_info *vi, struct receive_queue *rq,
> }
>
> static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
> - struct ewma_pkt_len *avg_pkt_len)
> + struct ewma_pkt_len *avg_pkt_len,
> + unsigned int room)
> {
> const size_t hdr_len = sizeof(struct virtio_net_hdr_mrg_rxbuf);
> unsigned int len;
>
> - len = hdr_len + clamp_t(unsigned int, ewma_pkt_len_read(avg_pkt_len),
> + if (room)
> + return PAGE_SIZE - room;
> +
> + len = hdr_len + clamp_t(unsigned int, ewma_pkt_len_read(avg_pkt_len),
> rq->min_buf_len, PAGE_SIZE - hdr_len);
> +
> return ALIGN(len, L1_CACHE_BYTES);
> }
>
> @@ -1028,21 +1049,27 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> {
> struct page_frag *alloc_frag = &rq->alloc_frag;
> unsigned int headroom = virtnet_get_headroom(vi);
> + unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> + unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> char *buf;
> void *ctx;
> int err;
> unsigned int len, hole;
>
> - len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len);
> - if (unlikely(!skb_page_frag_refill(len + headroom, alloc_frag, gfp)))
> + /* Extra tailroom is needed to satisfy XDP's assumption. This
> + * means rx frags coalescing won't work, but consider we've
> + * disabled GSO for XDP, it won't be a big issue.
> + */
> + len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> + if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> return -ENOMEM;
>
> buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> buf += headroom; /* advance address leaving hole at front of pkt */
> get_page(alloc_frag->page);
> - alloc_frag->offset += len + headroom;
> + alloc_frag->offset += len + room;
> hole = alloc_frag->size - alloc_frag->offset;
> - if (hole < len + headroom) {
> + if (hole < len + room) {
> /* To avoid internal fragmentation, if there is very likely not
> * enough space for another buffer, add the remaining space to
> * the current buffer.
> @@ -2576,12 +2603,15 @@ static ssize_t mergeable_rx_buffer_size_show(struct netdev_rx_queue *queue,
> {
> struct virtnet_info *vi = netdev_priv(queue->dev);
> unsigned int queue_index = get_netdev_rx_queue_index(queue);
> + unsigned int headroom = virtnet_get_headroom(vi);
> + unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> struct ewma_pkt_len *avg;
>
> BUG_ON(queue_index >= vi->max_queue_pairs);
> avg = &vi->rq[queue_index].mrg_avg_pkt_len;
> return sprintf(buf, "%u\n",
> - get_mergeable_buf_len(&vi->rq[queue_index], avg));
> + get_mergeable_buf_len(&vi->rq[queue_index], avg,
> + SKB_DATA_ALIGN(headroom + tailroom)));
> }
>
> static struct rx_queue_attribute mergeable_rx_buffer_size_attribute =
> --
> 2.7.4
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