From 6ee57bcc1e61d39c0579438055bc84087210f9b6 Mon Sep 17 00:00:00 2001 From: "Michael S. Tsirkin" Date: Tue, 16 Oct 2012 23:56:14 +1030 Subject: [PATCH] virtio-net: correct capacity math on ring full 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 Signed-off-by: Rusty Russell Acked-by: Michael S. Tsirkin --- drivers/net/virtio_net.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index cbf8b06..3db6586 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -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); -- 2.7.4