virtio-net: correct capacity math on ring full (6ee57bcc) · Commits · 戴 / test

Capacity math on ring full is wrong: we are looking at num_sg but that might be optimistic because of indirect buffer use. The implementation also penalizes fast path with extra memory accesses for the benefit of ring full condition handling which is slow path. It's easy to query ring capacity so let's do just that. This change also makes it easier to move vnet header for tx around as follow-up patch does. Signed-off-by:

Michael S. Tsirkin <mst@redhat.com> Signed-off-by:

Rusty Russell <rusty@rustcorp.com.au> Acked-by:

Michael S. Tsirkin <mst@redhat.com>

drivers/net/virtio_net.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -557,10 +557,10 @@ again:
		return received;
		}

		static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
		static void free_old_xmit_skbs(struct virtnet_info *vi)
		{
		struct sk_buff *skb;
		unsigned int len, tot_sgs = 0;
		unsigned int len;
		struct virtnet_stats *stats = this_cpu_ptr(vi->stats);

		while ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
		@@ -571,10 +571,8 @@ static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
		stats->tx_packets++;
		u64_stats_update_end(&stats->tx_syncp);

		tot_sgs += skb_vnet_hdr(skb)->num_sg;
		dev_kfree_skb_any(skb);
		}
		return tot_sgs;
		}

		static int xmit_skb(struct virtnet_info vi, struct sk_buff skb)
		@@ -664,7 +662,8 @@ static netdev_tx_t start_xmit(struct sk_buff skb, struct net_device dev)
		netif_stop_queue(dev);
		if (unlikely(!virtqueue_enable_cb_delayed(vi->svq))) {
		/* More just got used, free them then recheck. */
		capacity += free_old_xmit_skbs(vi);
		free_old_xmit_skbs(vi);
		capacity = vi->svq->num_free;
		if (capacity >= 2+MAX_SKB_FRAGS) {
		netif_start_queue(dev);
		virtqueue_disable_cb(vi->svq);

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