RE: [PATCH v4] virtio-net: enable configurable tx queue size

["Wang, Wei W" <wei.w.wang@intel.com>]

On Thursday, July 6, 2017 9:49 PM, Michael S. Tsirkin wrote:
> On Wed, Jun 28, 2017 at 10:37:59AM +0800, Wei Wang wrote:
> > This patch enables the virtio-net tx queue size to be configurable
> > between 256 (the default queue size) and 1024 by the user when the
> > vhost-user backend is used.
> >
> > Currently, the maximum tx queue size for other backends is 512 due to
> > the following limitations:
> > - QEMU backend: the QEMU backend implementation in some cases may send
> > 1024+1 iovs to writev.
> > - Vhost_net backend: there are possibilities that the guest sends a
> > vring_desc of memory which crosses a MemoryRegion thereby generating
> > more than 1024 iovs after translation from guest-physical address in
> > the backend.
> >
> > Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> 
> Could you pls add a bit info about how this was tested?
> Was any special setup for dpdk necessary?

Yes, I used the vhost-user implementation in DPDK. So, on the host, I have 
the legacy ovs-dpdk setup ready (I'm using dpdk-stable-16.11.1 and openvswitch-2.6.1,
the setup steps can be found inside the source code directory).

When booting the guest, I have the following QEMU commands:
-chardev socket,id=char1,path=/usr/local/var/run/openvswitch/vhost-user-1
-netdev type=vhost-user,id=mynet1,chardev=char1,vhostforce
-device virtio-net-pci,mac=52:54:00:00:00:01,netdev=mynet1,tx_queue_size=1024

To check the guest tx queue size, I simply added a printk() at the end of virtnet_probe()
to print out vi->sq->vq->num_free, which initially equals to the queue size.

Then, I did Ping and netperf tests to transmit packets between VMs, which worked fine.

If the related configuration support to Libvirt is ready, I think we can get the customer
to try in their test environment, too.

Best,
Wei