Work is underway to add per-virtqueue IOThread mapping to QEMU's virtio-blk and virtio-scsi devices.

Currently each device instance can be associated with just one IOThread where all virtqueues are processed. This is known to be a bottleneck and prevents true multi-queue operation because all I/O requests are funneled through a single IOThread on the host.

The new multi-queue support in QEMU will allow individual virtqueues to be mapped to an IOThread. It is likely that most users will wish to spread virtqueues round-robin across a set of IOThreads.

New domain XML syntax is necessary to expose this feature once it becomes available in QEMU.

I am filing this BZ now so there is time to discuss the feature and so that libvirt support can be developed in parallel to QEMU.