Virtual private caches

• Authors: Kyle J. Nesbit;James Laudon;James E. Smith
• Venue: Proceedings of the 34th annual international symposium on Computer architecture
• Year: 2007

Virtual Private Machines (VPM) provide a framework for Quality of Service (QoS) in CMP-based computer systems. VPMs incorporate microarchitecture mechanisms that allow shares of hardware resources to be allocated to executing threads, thus providing applications with an upper bound on execution time regardless of other thread activity. Virtual Private Caches (VPCs) are an important element of VPMs. VPC hardware consists of two major components: the VPC Arbiter, which manages shared cache bandwidth, and the VPC Capacity Manager, which manages the cache storage. Both the VPC Arbiter and VPC Capacity Manager provide minimum service guarantees that, when combined, achieve QoS for the cache subsystem. Simulation-based evaluation shows that conventional cache bandwidth management policies allow concurrently executing threads to affect each other significantly in an uncontrollable manner. The evaluation targets cache bandwidth because the effects of cache capacity sharing have been studied elsewhere. In contrast with the conventional policies, the VPC Arbiter meets its QoS performance objectives on all workloads studied and over a range of allocated bandwidth levels. The VPC Arbiter’s fairness policy, which distributes leftover bandwidth, mitigates the effects of cache preemption latencies, thus ensuring threads a high-degree of performance isolation. Furthermore, the VPC Arbiter eliminates negative bandwidth interference which can improve aggregate throughput and resource utilization.