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

[Mario Smarduch]

Public bug reported:

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.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1286253

Title:
  virtio-net acceleration features not set when plugged into backend
  dynamically

Status in QEMU:
  New

Bug description:
  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.

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