KVM Forum 2014

Over the past year core parts of QEMU have been extended to support multi-threaded device emulation. This has enabled a rewrite of the experimental virtio-blk dataplane feature so that multi-threaded device emulation can become a fully-supported feature of QEMU. Although work is still ongoing, virtio-blk device emulation can now run in dedicated threads, called iothreads. These threads can be bound to host CPUs much in the same way that vCPUs can be bound. This makes it possible to achieve better scalability on multicore hosts where QEMU's legacy global mutex presents a bottleneck. This talk covers new thread-friendly infrastructure in QEMU and how it is used in virtio-blk. It also presents performance results showing the effect of multi-threaded device emulation. Finally, it outlines the remaining work and the new possibilities for multiqueue devices.