Re: [Qemu-devel] [snabb-devel] Re: [PATCH v6 1/2] vhost-user: add multi queue support

[Michael S. Tsirkin]

On Tue, Sep 01, 2015 at 05:20:06PM +0800, Yuanhan Liu wrote:
> On Mon, Aug 31, 2015 at 02:30:06PM +0300, Michael S. Tsirkin wrote:
> [snip..] 
> > > Then how about the other case:
> > > When startup the vhost backend, user specify 8 queues, like:
> > > Vhost-user ...  -queues 8      # Y=8
> > > When startup the guest, user specify 4 queues, like:
> > > Qemu-kvm ... -queues 4      # X=4
> > > 
> > > Vhost backend CAN support the queues number as much as the guest/qemu 
> > > requires,
> > > And qemu don't want enable all of them(8 in the case), just part of 
> > > them(only 4 from 8).
> > > Will qemu exit or go forward(of course with 4 queues)? 
> > 
> > I think it must go forward since guest does not have to
> > configure all queues anyway - and that's built in to virtio spec.
> > 
> > Note that # of queues in actual use in fact changes dynamically
> > too, without restaring the device.
> 
> May I know how do you do that? I mean, is there a public interface, like
> by some commands? Or, by sending vhost messages?
> 
>       --yliu

Using ethtool within guest. In fact, guests boot with a single queue,
you need to use ethtool to enable mq, specifying the # of queues.

-- 
MST