Re: [Qemu-devel] [question] virtio-net-device and multi-queue option

[Gonglei (Arei)]

> From: Eric Auger [mailto:address@hidden
> Sent: Friday, September 19, 2014 10:23 AM
> To: Gonglei (Arei); qemu list; Michael S. Tsirkin
> Subject: Re: [Qemu-devel] [question] virtio-net-device and multi-queue option
> 
> On 09/19/2014 03:42 AM, Gonglei (Arei) wrote:
> >> Subject: [Qemu-devel] [question] virtio-net-device and multi-queue option
> >>
> >> Hi,
> >>
> >>
> >> I am currently doing some benchmarks using virtio-net-device using
> >> virtio-mmio (non PCI) with qemu_system_arm with KVM. Purpose is to
> >> compare with device passthrough performance.
> >>
> >> I heard about the availability of a multi-queue option that greatly
> >> improves the performance but I currently fail in enabling it.
> >>
> >> Please could someone explain me how to turn that feature on? My current
> >> virtio-net options simply are:
> >>
> >>         -netdev tap,id=tap0,ifname="tap0" \
> >>         -device virtio-net-device,netdev=tap0
> >>
> >
> > There are some steps:
> >
> >  1. create multi-queue netdev device, such as tap device (you can
> >    use "ip tuntap" command, or libvirt), something like as below:
> >     ip tuntap add tap_1 mode tap multi_queue
> >  2. pass corresponding parameters in QEMU command line:
> >    -netdev
> type=tap,ifname=tap_q,id=net1,vhost=on,vhostforce=on,queues=4,script= \
> >    -device virtio-net-device,netdev=net1,mq=on,vectors=9
> 
> Hi Gonglei,
> 
> Thanks for your quick reply.
> 
> Definitively I have not gone through step 1! Nethertheless I am a but
> dubious about the fact the mq property does not seem to exist for my
> virtio-net-device. I get
> 
> qemu-system-arm: -device
> virtio-net-device,netdev=tap0,mq=on,mac=52:54:00:12:34:56: Property
> '.mq' not found
> 
Sorry, my typo. :(

It should be "virtio-net-pci", not "virtio-net-devcie" 

BTW, You can use help command to get a devices properties:

# ./qemu-system-x86_64 -device virtio-net-pci,? 
[...] 
virtio-net-pci.mq=on/off
[...]

Best regards,
-Gonglei

> Best Regards
> 
> Eric
> >
> >> Also are there any "easy" tunings I can play with to try to reach the
> >> best performance.
> >>
> >
> > You can consider that using irq binding, core binding, vhost-net? etc..
> >
> > Best regards,
> > -Gonglei
> >
> >> Thank you in advance
> >>
> >> Best Regards
> >>
> >> Eric
> >