On Mon, 27 Apr 2020 15:21:02 +0800 Jason Wang <jasowang@xxxxxxxxxx> wrote: > On 2020/4/23 上午12:09, 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 <jasowang@xxxxxxxxxx> > > Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> > > --- > > 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; > > > Should this be PAGE_SIZE - SKB_DATA_ALIGN(sizeof(struct skb_shared_info))? No, frame_sz include the SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) length. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
