Re: vhost + multiqueue + RSS question.

[Gleb Natapov <gleb@cloudius-systems.com>]

On Sun, Nov 16, 2014 at 08:56:04PM +0200, Michael S. Tsirkin wrote:
> On Sun, Nov 16, 2014 at 06:18:18PM +0200, Gleb Natapov wrote:
> > Hi Michael,
> > 
> >  I am playing with vhost multiqueue capability and have a question about
> > vhost multiqueue and RSS (receive side steering). My setup has Mellanox
> > ConnectX-3 NIC which supports multiqueue and RSS. Network related
> > parameters for qemu are:
> > 
> >    -netdev tap,id=hn0,script=qemu-ifup.sh,vhost=on,queues=4
> >    -device virtio-net-pci,netdev=hn0,id=nic1,mq=on,vectors=10
> > 
> > In a guest I ran "ethtool -L eth0 combined 4" to enable multiqueue.
> > 
> > I am running one tcp stream into the guest using iperf. Since there is
> > only one tcp stream I expect it to be handled by one queue only but
> > this seams to be not the case. ethtool -S on a host shows that the
> > stream is handled by one queue in the NIC, just like I would expect,
> > but in a guest all 4 virtio-input interrupt are incremented. Am I
> > missing any configuration?
> 
> I don't see anything obviously wrong with what you describe.
> Maybe, somehow, same irqfd got bound to multiple MSI vectors?
It does not look like this is what is happening judging by the way
interrupts are distributed between queues. They are not distributed
uniformly and often I see one queue gets most interrupt and others get
much less and then it changes.

--
			Gleb.