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virtio-net: avoid unnecessary sg initialzation

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Usually an skb does not have up to MAX_SKB_FRAGS frags. So no need to
initialize the unuse part of sg. This patch initialize the sg based on
the real number it will used:

- during xmit, it could be inferred from nr_frags and can_push.
- for small receive buffer, it will also be 2.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jason Wang 2015-08-27 14:53:06 +08:00 committed by David S. Miller
parent 5e0aa59728
commit 547c890cfd
1 changed files with 2 additions and 2 deletions
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4
drivers/net/virtio_net.c
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@ -540,7 +540,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
skb_put(skb, GOOD_PACKET_LEN);
hdr = skb_vnet_hdr(skb);
sg_init_table(rq->sg, MAX_SKB_FRAGS + 2);
sg_init_table(rq->sg, 2);
sg_set_buf(rq->sg, hdr, vi->hdr_len);
skb_to_sgvec(skb, rq->sg + 1, 0, skb->len);
@ -893,7 +893,7 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
if (vi->mergeable_rx_bufs)
hdr->num_buffers = 0;
sg_init_table(sq->sg, MAX_SKB_FRAGS + 2);
sg_init_table(sq->sg, skb_shinfo(skb)->nr_frags + (can_push ? 1 : 2));
if (can_push) {
__skb_push(skb, hdr_len);
num_sg = skb_to_sgvec(skb, sq->sg, 0, skb->len);