Mitigating performance unpredictability in the IaaS using the Kyoto principle

Performance isolation is enforced in the cloud by setting to each virtual machine (VM) a given fraction of each resource type (physical memory, processor, and IO bandwidth). However, microarchitectural-level resources such as processor's caches cannot be divided and allocated to VMs: they are globally shared among all VMs which compete for their use, leading to cache contention. Therefore, performance isolation and predictability are compromised. This situation is devastating for HPC applications. In this paper, we propose a software solution (called Kyoto) to this issue, inspired by the polluters pay principle. A VM is said to pollute the cache if it provokes significant cache replacements which impact the performance of other VMs. Henceforth, using the Kyoto system, the provider can encourage HPC cloud users to book pollution permits for their VMs. We have implemented Kyoto in several virtualization systems including both general purpose systems (Xen and KVM) and specialized HPC systems (Pisces).