Re: [kvm-devel] [PATCH] Increase the tx queue to 512 descriptors to fix performance problem.

[Dor L. <dor...@gm...>]

On Wed, 2008-01-09 at 08:29 -0600, Anthony Liguori wrote:
> Dor Laor wrote:
> > Now that we have a host timer based tx wakeup it waits for 64
> > packets or timeout before processing them.
> > This might cause the guest to run out of tx buffers while the host
> > holds them up.
> >   
> 
> There's a proper fix that Rusty added last night.

This is with his latest patch, without it I got a lot of
"printk("Unlikely: restart svq failed\n");"
+ The performance is much better now.

> 
> > This is a temporal solution to quickly bring back performance to 800mbps.
> > But a better fix will soon be sent (its not the only problem).
> >   
> 
> How are you doing performance testing?

Not really, this was just to stabilize the module.
It needs some more work, disable/enable of the device is broken.

> 
> Regards,
> 
> Anthony Liguori
> 
> > Signed-off-by: Dor Laor <dor...@qu...>
> > ---
> >  qemu/hw/virtio-net.c |    2 +-
> >  1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
> > index 777fe2c..3d07b65 100644
> > --- a/qemu/hw/virtio-net.c
> > +++ b/qemu/hw/virtio-net.c
> > @@ -293,7 +293,7 @@ void *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn)
> >      n->vdev.update_config = virtio_net_update_config;
> >      n->vdev.get_features = virtio_net_get_features;
> >      n->rx_vq = virtio_add_queue(&n->vdev, 512, virtio_net_handle_rx);
> > -    n->tx_vq = virtio_add_queue(&n->vdev, 128, virtio_net_handle_tx);
> > +    n->tx_vq = virtio_add_queue(&n->vdev, 512, virtio_net_handle_tx);
> >      n->can_receive = 0;
> >      memcpy(n->mac, nd->macaddr, 6);
> >      n->vc = qemu_new_vlan_client(nd->vlan, virtio_net_receive,
> >   
>