Maximizing VMs’ IO Performance on Overcommitted CPUs with Fairness

Abstract

To improve resource utilization and reduce costs many Cloud providers adopt virtual machines (VMs) overcommitment. While effective, this strategy may lead to adverse outcomes, significantly affecting a VM IO performance when one virtual CPU (vCPU) is preempted by another vCPU within the same runqueue of the VM scheduler – i.e., same physical CPU (pCPU). Additionally, the responsiveness of a VM is reduced during the inactive time of the vCPU, and it necessitates an extra schedule timeslice to react to any IO event. While such problems have been studied in academia and industry, no previous solution has been deployed in production. This is because for example certain solutions require modifications of the guest VM, which is in contrast with industry requirements. We propose Anubis, a new IO-aware VM scheduler targeting Linux KVM, the most popular VMM in today’s Clouds, without requiring any guest VM modifications. Anubis shortens the IO event pending time by lightweight monitoring IO events including interrupt delivery and KVM exit. For the vCPU running the IO activity, Anubis provides an accurate boost, which is exclusively active only during the period when the vCPU has IO activity. While the IO performance is maximized, Anubis still guarantees fairness among VMs. The vCPU that doesn’t have IO activity and belongs to the same VM will voluntarily yield the computing resources to counterbalance the unfairness created by the vCPU that has been given a performance boost. Overall, Anubis is a practical_solution that provides close-to-non-overcommit_performance for IO workloads in VM overcommitted scenarios.