Re: vhost-net patches

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Oct 19, 2009 at 03:56:54PM -0700, Sridhar Samudrala wrote:
> On Sun, 2009-10-18 at 19:32 +0200, Michael S. Tsirkin wrote:
> > On Sun, Oct 18, 2009 at 12:53:56PM +0200, Michael S. Tsirkin wrote:
> > > On Fri, Oct 16, 2009 at 12:29:29PM -0700, Sridhar Samudrala wrote:
> > > > Hi Michael,
> > > > 
> > > > We are trying out your vhost-net patches from your git trees on kernel.org.
> > > > I am using mst/vhost.git as host kernel and mst/qemu-kvm.git for qemu.
> > > > 
> > > > I am using the following qemu script to start the guest using userspace tap backend.
> > > > 
> > > > home/sridhar/git/mst/qemu-kvm/x86_64-softmmu/qemu-system-x86_64 /home/sridhar/kvm_images/fedora10-1-vm -m 512 -drive file=/home/sridhar/kvm_images/fedora10-1-vm,if=virtio,index=0,boot=on -net nic,macaddr=54:52:00:35:e3:73,model=virtio -net tap,ifname=vnet0,script=no,downscript=no
> > > > 
> > > > Now that i got the default backend to work, i wanted to try vhost in kernel. But
> > > > could not figure out the right -net option to pass to qemu.
> > > > 
> > > > Can you let me know the right syntax to start a guest using vhost.
> > > > 
> > > > Thanks
> > > > Sridhar
> > > 
> > > Here's an example with raw socket:
> > > 
> > > /root/kvm-test/bin/qemu-system-x86_64 -m 1G -kernel \
> > > /boot/vmlinuz-$release -append \
> > > 'root=UUID=d5d2d201-d086-42ad-bb1d-32fbe40eda71 ro quiet nosplash \
> > > console=tty0 console=ttyS0,9600n8' -initrd /boot/guest-initrd.img \
> > > $HOME/disk.raw.copy -net raw,ifname=eth3 -net nic,model=virtio,vhost \
> > > -balloon none -redir tcp:8023::22
> > > 
> > > As you see, I changed the command line.
> > > You now simply add ",vhost" after model, and it will locate
> > > host network interface specified earlier and attach to it.
> > > This should have been clear from running  qemu with -help
> > > flag. Could you please suggest how can that text
> > > be clarified?
> 
> I updated to your latest git trees and the default user-space tap backend using the
> following -net options worked fine.
> -net tap,ifname=vnet0,script=no,downscript=no -net nic,model=virtio
> 
> But i could not get vhost to work with either raw or tap backends.
> I tried the following combinations.
> 1) -net raw,ifname=eth0 -net nic,model=virtio,vhost
> 2) -net raw,ifname=vnet0, -net nic,model=virtio,vhost
> 3) -net tap,ifname=vnet0,script=no,downscript=no -net nic,model=virtio,vhost
> 
> They all failed with the following error
>     vhost_net_init returned -7
> This is an error message from hw/virtio-net.c:virtio_net_driver_ok() when
> vhost_net_start() fails. It looks like dev->binding->irqfd() is failing in
> vhost_virtqueue_init(). Haven't yet debugged further. I have CONFIG_EVENTFD
> enabled in the host kernel.
> 
> Are all the above -net options supposed to work?
> 
> In your descriptions, you say that checksum/tso offload is not supported.

They should work with tap but not raw sockets yet.

> Isn't it
> possible to send/receive large packets without checksum using AF_PACKET sockets if
> the attached interface supports these offloads.
> Do you see the same offload issue even when using tap backend via vhost?
> 
> Thanks
> Sridhar
> 
> 
> 
> 
> 
>