Re: [Qemu-discuss] [Qemu-devel] Throttle in virtio-net

[Daniel P. Berrange]

On Mon, Sep 05, 2016 at 10:52:40AM +0200, Pradeep Kiruvale wrote:
> Hi Alberto,
> 
> Thanks for your reply.
> 
> >
> > > I am planning to implement throttling functionality for virtio-net
> > > driver using the throttling APIs that exist inside qemu.
> >
> > Hi Pradeep,
> >
> > the problem with implementing throttling for the network is that
> > it's useless if you use the vhost_net kernel accelerator, because it
> > bypasses QEMU entirely:
> >
> >    https://access.redhat.com/documentation/en-US/Red_Hat_
> > Enterprise_Linux/7/html/Virtualization_Tuning_and_Optimization_Guide/sect-
> > Virtualization_Tuning_Optimization_Guide-Networking-
> > Virtio_and_vhostnet.html
> 
> 
> Thanks for this very valuable information. What if someone wants to just
> use virtio-net without the vhost acceleration?
> Any idea how it will be done in this case? It still uses cgroup or some
> other mechanism to do throttling?
> 
> >
> > libvirt implements this using tc:
> >
> >    https://libvirt.org/formatdomain.html#elementDomain
> >    http://luxik.cdi.cz/~devik/qos/htb/manual/userg.htm#ceiling
> 
> 
> Here it uses the cgroup inside the libvirt dirver to control the packet
> rate right?

No, cgroups is not involved. Libvirt attaches a tc filter directly to
the host TAP device associated with the virtual NIC.

Cgroups tc support would only be relevant if you're trying to filter
non-NIC related network traffic QEMU generates.

Regards,
Daniel
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