On Thu, Apr 30, 2020 at 01:22:08PM +0200, Jesper Dangaard Brouer wrote: > The virtio_net driver is running inside the guest-OS. There are two > XDP receive code-paths in virtio_net, namely receive_small() and > receive_mergeable(). The receive_big() function does not support XDP. > > In receive_small() the frame size is available in buflen. The buffer > backing these frames are allocated in add_recvbuf_small() with same > size, except for the headroom, but tailroom have reserved room for > skb_shared_info. The headroom is encoded in ctx pointer as a value. > > In receive_mergeable() the frame size is more dynamic. There are two > basic cases: (1) buffer size is based on a exponentially weighted > moving average (see DECLARE_EWMA) of packet length. Or (2) in case > virtnet_get_headroom() have any headroom then buffer size is > PAGE_SIZE. The ctx pointer is this time used for encoding two values; > the buffer len "truesize" and headroom. In case (1) if the rx buffer > size is underestimated, the packet will have been split over more > buffers (num_buf info in virtio_net_hdr_mrg_rxbuf placed in top of > buffer area). If that happens the XDP path does a xdp_linearize_page > operation. > > Cc: Jason Wang <[email protected]> > Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]> > --- > drivers/net/virtio_net.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 11f722460513..1df3676da185 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -689,6 +689,7 @@ static struct sk_buff *receive_small(struct net_device > *dev, > xdp.data_end = xdp.data + len; > xdp.data_meta = xdp.data; > xdp.rxq = &rq->xdp_rxq; > + xdp.frame_sz = buflen; > orig_data = xdp.data; > act = bpf_prog_run_xdp(xdp_prog, &xdp); > stats->xdp_packets++; > @@ -797,10 +798,11 @@ static struct sk_buff *receive_mergeable(struct > net_device *dev, > int offset = buf - page_address(page); > struct sk_buff *head_skb, *curr_skb; > struct bpf_prog *xdp_prog; > - unsigned int truesize; > + unsigned int truesize = mergeable_ctx_to_truesize(ctx); > unsigned int headroom = mergeable_ctx_to_headroom(ctx); > - int err; > unsigned int metasize = 0; > + unsigned int frame_sz; > + int err; > > head_skb = NULL; > stats->bytes += len - vi->hdr_len; > @@ -821,6 +823,11 @@ static struct sk_buff *receive_mergeable(struct > net_device *dev, > if (unlikely(hdr->hdr.gso_type)) > goto err_xdp; > > + /* Buffers with headroom use PAGE_SIZE as alloc size, > + * see add_recvbuf_mergeable() + get_mergeable_buf_len() > + */ > + frame_sz = headroom ? PAGE_SIZE : 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 > @@ -834,6 +841,8 @@ static struct sk_buff *receive_mergeable(struct > net_device *dev, > page, offset, > VIRTIO_XDP_HEADROOM, > &len); > + frame_sz = PAGE_SIZE; > + > if (!xdp_page) > goto err_xdp; > offset = VIRTIO_XDP_HEADROOM; > @@ -850,6 +859,7 @@ static struct sk_buff *receive_mergeable(struct > net_device *dev, > xdp.data_end = xdp.data + (len - vi->hdr_len); > xdp.data_meta = xdp.data; > xdp.rxq = &rq->xdp_rxq; > + xdp.frame_sz = frame_sz; > > act = bpf_prog_run_xdp(xdp_prog, &xdp); > stats->xdp_packets++; > @@ -924,7 +934,6 @@ static struct sk_buff *receive_mergeable(struct > net_device *dev, > } > rcu_read_unlock(); > > - truesize = mergeable_ctx_to_truesize(ctx); > if (unlikely(len > truesize)) { > pr_debug("%s: rx error: len %u exceeds truesize %lu\n", > dev->name, len, (unsigned long)ctx); > >
