"Michael S. Tsirkin" <m...@redhat.com> writes: > On Thu, Aug 16, 2012 at 10:20:05AM +0100, Chris Webb wrote: > > > For example, I can run > > > > ip addr add 192.168.1.2/24 dev eth0 > > ip link set eth0 up > > ip link add link eth0 name tap0 address 02:02:02:02:02:02 type macvtap > > mode bridge > > ip link set tap0 up > > qemu-kvm -hda debian.img -cpu host -m 512 -vnc :0 \ > > -net nic,model=virtio,macaddr=02:02:02:02:02:02 \ > > -net tap,fd=3 3<>/dev/tap$(< /sys/class/net/tap0/ifindex) > > > > on one physical host which is otherwise completely idle. From a second > > physical host on the same network, I then scp a large (say 50MB) file onto > > the new guest. On a gigabit LAN, speeds consistently drop to less than > > 100kB/s as the transfer progresses, within a second of starting.
> Thanks for the report. > I'll try to reproduce this early next week. > Meanwhile a question - do you still observe this behaviour if you enable > vhost-net? I haven't tried running with vhost-net before. Is it sufficient to compile the host kernel with CONFIG_VHOST_NET=y and boot the guest with qemu-kvm -hda debian.img -cpu host -m 512 -vnc :0 \ -net nic,model=virtio,macaddr=02:02:02:02:02:02 \ -net tap,fd=3,vhost=on,vhostfd=4 \ 3<>/dev/tap$(< /sys/class/net/tap0/ifindex) 4<>/dev/vhost-net ? If so, then I'm afraid this doesn't make any difference: it still stalls and drops right down in speed. The reason I'm hesitant about whether the vhost-net is actually working is that with both vhost=off and vhost=on, I see an identical virtio feature set within the guest: # cat /sys/bus/virtio/devices/virtio0/features 0000011000000001111100000000100000000000000000000000000000000000 However, without the 4<>/dev/vhost-net or with 4<>/dev/null, it seems to fail to start altogether with vhost=on,vhostfd=4, so perhaps it's fine? Cheers, Chris.