mClock: Handling Throughput Variability for Hypervisor IO Scheduling

Virtualized servers run a diverse set of Virtual Machines (VMs), ranging from interactive desktops to test and development environments and even batch workloads. Hypervisors are responsible for multiplexing the underlying hardware resources among VMs while providing them the desired degree of isolation using resource management controls. Existing methods provide many knobs for allocating CPU and memory to VMs, but support for control of IO resource allocation has been quite limited. IO resource management in a hypervisor introduces significant new challenges and needs more extensive controls than in commodity operating systems. This paper introduces a novel algorithm for IO resource allocation in a hypervisor. The algorithm, mClock, supports proportional-share fairness subject to minimum reservations and maximum limits on the IO allocations for VMs.