Re: [Qemu-devel] [Bug 1286253] [NEW] virtio-net acceleration features not set when plugged into backend dynamically

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Feb 28, 2014 at 05:40:19PM -0000, Mario Smarduch wrote:
> When using indpendent transport and backend in this case virtio-net-
> device transport, none of the acceleration features are set after guest
> probes the transport the backend is plugged into. For virtio-net this
> leads to low throughput/performance.  This holds true for  virtio-mmio,
> PCI transports and most likely for others as well (CCW, S390) and other
> backends
> 
> Command to run:
> ./qemu-system-arm -enable-kvm -smp 2 -kernel zImage -dtb ./guest-a15.dtb -m 512 -M vexpress-a15 -cpu cortex-a15 -nographic \
>       -append "root=/dev/vda rw console=ttyAMA0 rootwait" -drive if=none,file=/mnt/gauss.root,id=vm1 \
>       -device virtio-blk-device,drive=vm1 -netdev type=tap,id=net0,ifname=tap0 \
>       -device virtio-net-device,netdev=net0,mac="52:54:00:12:34:58"
> 
> For x86 same virtio command for network.

Can you explain in more detail?

The command-line looks sane.  The virtio-net-device instance should
figure out the tap supports offloads.

Did you try adding a printf to virtio_net_get_features() to see why the
offload features are not being detected?

Stefan