A Framework for Providing Quality of Service in Chip Multi-Processors

The trends in enterprise IT toward service-oriented computing, server consolidation, and virtual computing point to a future in which workloads are becoming increasingly diverse in terms of performance, reliability, and availability requirements. It can be expected that more and more applications with diverse requirements will run on a CMP and share platform resources such as the lowest level cache and off-chip bandwidth. In this environment, it is desirable to have microarchitecture and software support that can provide a guarantee of a certain level of performance, which we refer to as performance Quality of Service. In this paper, we investigate a framework that would be needed for a CMP to fully provide QoS. We found that the ability of a CMP to partition platform resources alone is not sufficient for fully providing QoS. We also need an appropriate way to specify a QoS target, and an admission control policy that accepts jobs only when their QoS targets can be satisfied. We also found that providing strict QoS often leads to a significant reduction in throughput due to resource fragmentation. We propose novel throughput optimization techniques that include: (1) exploiting various QoS execution modes, and (2) a microarchitecture technique that steals excess resources from a job while still meeting its QoS target. We evaluated our QoS framework with a full system simulation of a 4-core CMP and a recent version of the Linux Operating System. We found that compared to an unoptimized scheme, the throughput can be improved by up to 47%, making the throughput significantly closer to a non-QoS CMP.