在 2022/12/27 下午2:46, Jason Wang 写道:
在 2022/12/20 22:14, Heng Qi 写道:
Support xdp for multi buffer packets in mergeable mode.
Putting the first buffer as the linear part for xdp_buff,
and the rest of the buffers as non-linear fragments to struct
skb_shared_info in the tailroom belonging to xdp_buff.
Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
drivers/net/virtio_net.c | 78 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 08f209d7b0bf..8fc3b1841d92 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -931,6 +931,84 @@ static struct sk_buff *receive_big(struct
net_device *dev,
return NULL;
}
+/* TODO: build xdp in big mode */
+static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
+ struct virtnet_info *vi,
+ struct receive_queue *rq,
+ struct xdp_buff *xdp,
+ void *buf,
+ unsigned int len,
+ unsigned int frame_sz,
+ u16 *num_buf,
+ unsigned int *xdp_frags_truesize,
+ struct virtnet_rq_stats *stats)
+{
+ unsigned int tailroom = SKB_DATA_ALIGN(sizeof(struct
skb_shared_info));
+ struct virtio_net_hdr_mrg_rxbuf *hdr = buf;
+ unsigned int truesize, headroom;
+ struct skb_shared_info *shinfo;
+ unsigned int xdp_frags_truesz = 0;
+ unsigned int cur_frag_size;
+ struct page *page;
+ skb_frag_t *frag;
+ int offset;
+ void *ctx;
+
+ xdp_init_buff(xdp, frame_sz, &rq->xdp_rxq);
+ xdp_prepare_buff(xdp, buf - VIRTIO_XDP_HEADROOM,
+ VIRTIO_XDP_HEADROOM + vi->hdr_len, len - vi->hdr_len,
true);
+
+ if (*num_buf > 1) {
+ shinfo = xdp_get_shared_info_from_buff(xdp);
+ shinfo->nr_frags = 0;
+ shinfo->xdp_frags_size = 0;
+ }
+
+ if ((*num_buf - 1) > MAX_SKB_FRAGS)
+ return -EINVAL;
+
+ while ((--*num_buf) >= 1) {
+ buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
+ if (unlikely(!buf)) {
+ pr_debug("%s: rx error: %d buffers out of %d missing\n",
+ dev->name, *num_buf,
+ virtio16_to_cpu(vi->vdev, hdr->num_buffers));
+ dev->stats.rx_length_errors++;
+ return -EINVAL;
+ }
+
+ if (!xdp_buff_has_frags(xdp))
+ xdp_buff_set_frags_flag(xdp);
Any reason to put this inside the loop?
I'll move it outside the loop in the next version.
+
+ stats->bytes += len;
+ page = virt_to_head_page(buf);
+ offset = buf - page_address(page);
+ truesize = mergeable_ctx_to_truesize(ctx);
+ headroom = mergeable_ctx_to_headroom(ctx);
+
+ cur_frag_size = truesize + (headroom ? (headroom + tailroom)
: 0);
+ xdp_frags_truesz += cur_frag_size;
Not related to this patch, but it would easily confuse the future
readers that the we need another math for truesize. I think at least
we need some comments for this or
Yes it might, I'll add more comments on this.
I guess the root cause is in get_mergeable_buf_len:
static unsigned int get_mergeable_buf_len(struct receive_queue *rq,
struct ewma_pkt_len *avg_pkt_len,
unsigned int room)
{
struct virtnet_info *vi = rq->vq->vdev->priv;
const size_t hdr_len = vi->hdr_len;
unsigned int len;
if (room)
return PAGE_SIZE - room;
And we do
len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
...
ctx = mergeable_len_to_ctx(len, headroom);
I wonder if it's better to pack the real truesize (PAGE_SIZE) here.
This may ease a lot of things.
I don't know the historical reason for not packing, but I guess this is
for the convenience of
comparing the actual length len given by the device with truesize.
Therefore, I think it would
be better to keep the above practice for now? Perhaps, I can add more
explanation to the
above code to help future readers try not to get confused.
Thanks.
Thanks
+ if (unlikely(len > truesize || cur_frag_size > PAGE_SIZE)) {
+ pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
+ dev->name, len, (unsigned long)ctx);
+ dev->stats.rx_length_errors++;
+ return -EINVAL;
+ }
+
+ frag = &shinfo->frags[shinfo->nr_frags++];
+ __skb_frag_set_page(frag, page);
+ skb_frag_off_set(frag, offset);
+ skb_frag_size_set(frag, len);
+ if (page_is_pfmemalloc(page))
+ xdp_buff_set_frag_pfmemalloc(xdp);
+
+ shinfo->xdp_frags_size += len;
+ }
+
+ *xdp_frags_truesize = xdp_frags_truesz;
+ return 0;
+}
+
static struct sk_buff *receive_mergeable(struct net_device *dev,
struct virtnet_info *vi,
struct receive_queue *rq,
