Re: [PATCH net-next v3 5/8] virtio-net: xsk zero copy xmit support xsk unaligned mode

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在 2021/3/31 下午3:11, Xuan Zhuo 写道:
In xsk unaligned mode, the frame pointed to by desc may span two
consecutive pages, but not more than two pages.

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
Reviewed-by: Dust Li <dust.li@xxxxxxxxxxxxxxxxx>


I'd squash this patch into patch 4.


---
  drivers/net/virtio_net.c | 30 ++++++++++++++++++++++++------
  1 file changed, 24 insertions(+), 6 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index c8a317a93ef7..259fafcf6028 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2562,24 +2562,42 @@ static void virtnet_xsk_check_space(struct send_queue *sq)
  static int virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
  			    struct xdp_desc *desc)
  {
+	u32 offset, n, i, copy, copied;


Let's use a better name since we don't actually copy anything here.


  	struct virtnet_info *vi;
  	struct page *page;
  	void *data;
-	u32 offset;
+	int err, m;
  	u64 addr;
-	int err;
vi = sq->vq->vdev->priv;
  	addr = desc->addr;
+
  	data = xsk_buff_raw_get_data(pool, addr);
+
  	offset = offset_in_page(data);
+	m = desc->len - (PAGE_SIZE - offset);
+	/* xsk unaligned mode, desc will use two page */
+	if (m > 0)
+		n = 3;
+	else
+		n = 2;
- sg_init_table(sq->sg, 2);
+	sg_init_table(sq->sg, n);
  	sg_set_buf(sq->sg, &xsk_hdr, vi->hdr_len);
-	page = xsk_buff_xdp_get_page(pool, addr);
-	sg_set_page(sq->sg + 1, page, desc->len, offset);
- err = virtqueue_add_outbuf(sq->vq, sq->sg, 2, NULL, GFP_ATOMIC);
+	copied = 0;
+	for (i = 1; i < n; ++i) {
+		copy = min_t(int, desc->len - copied, PAGE_SIZE - offset);
+
+		page = xsk_buff_xdp_get_page(pool, addr + copied);
+
+		sg_set_page(sq->sg + i, page, copy, offset);
+		copied += copy;
+		if (offset)
+			offset = 0;
+	}


Can we simplify the codes by using while here? Then I think we don't need to determine the value of n.

Thanks


+
+	err = virtqueue_add_outbuf(sq->vq, sq->sg, n, NULL, GFP_ATOMIC);
  	if (unlikely(err))
  		sq->xsk.last_desc = *desc;

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