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Re: [Qemu-devel] Slow inbound traffic on macvtap interfaces
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] Slow inbound traffic on macvtap interfaces |
Date: |
Thu, 16 Aug 2012 18:36:13 +0300 |
On Thu, Aug 16, 2012 at 03:27:57PM +0100, Chris Webb wrote:
> "Michael S. Tsirkin" <address@hidden> 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
Yes that is expected.
> 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.