On Wed, Mar 09, 2011 at 08:25:34AM -0800, Shirley Ma wrote:
> On Wed, 2011-03-09 at 18:10 +0200, Michael S. Tsirkin wrote:
> >
> > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > index 82dba5a..4477b9a 100644
> > --- a/drivers/net/virtio_net.c
> > +++ b/drivers/net/virtio_net.c
> > @@ -514,11 +514,11 @@ static unsigned int free_old_xmit_skbs(struct
> > virtnet_info *vi)
> > struct sk_buff *skb;
> > unsigned int len, tot_sgs = 0;
> >
> > - while ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
> > + if ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
> > pr_debug("Sent skb %p\n", skb);
> > vi->dev->stats.tx_bytes += skb->len;
> > vi->dev->stats.tx_packets++;
> > - tot_sgs += skb_vnet_hdr(skb)->num_sg;
> > + tot_sgs = 2+MAX_SKB_FRAGS;
> > dev_kfree_skb_any(skb);
> > }
> > return tot_sgs;
> > @@ -576,7 +576,7 @@ static netdev_tx_t start_xmit(struct sk_buff *skb,
> > struct net_device *dev)
> > struct virtnet_info *vi = netdev_priv(dev);
> > int capacity;
> >
> > - /* Free up any pending old buffers before queueing new ones.
> > */
> > + /* Free up any old buffers so we can queue new ones. */
> > free_old_xmit_skbs(vi);
> >
> > /* Try to transmit */
> > @@ -605,6 +605,10 @@ static netdev_tx_t start_xmit(struct sk_buff
> > *skb, struct net_device *dev)
> > skb_orphan(skb);
> > nf_reset(skb);
> >
> > + /* Free up any old buffers so we can queue new ones. */
> > + if (capacity < 2+MAX_SKB_FRAGS)
> > + capacity += free_old_xmit_skbs(vi);
> > +
> > /* Apparently nice girls don't return TX_BUSY; stop the queue
> > * before it gets out of hand. Naturally, this wastes
> > entries. */
> > if (capacity < 2+MAX_SKB_FRAGS) {
> > --
>
> I tried this one as well. It might improve TCP_RR performance but not
> TCP_STREAM. :) Let's wait for Tom's TCP_RR resutls.
>
> Thanks
> Shirley
I think your issues are with TX overrun.
Besides delaying IRQ on TX, I don't have many ideas.
The one interesting thing is that you see better speed
if you drop packets. netdev crowd says this should not happen,
so could be an indicator of a problem somewhere.
--
MST
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