Protection, Utilization and Collaboration in Shared Cache Through Rationing

Shared cache is generally optimized to maximize the overall throughput, fairness, or both. Increasingly in shared environments, especially compute clouds, users are unrelated to one another. In such circumstances, an overall gain in throughput does not justify an individual loss. This paper explores conservative sharing, which protects the cache occupancy for individual programs, but still enables full cache sharing whenever there is unused space. Specifically, we present a new hardware based mechanism called cache rationing. Each core/program is assigned a portion of the shared cache as its ration. The hardware support protects the ration so it cannot be taken away by peer programs while in use. However, a program can exceed its allocated ration only if another program has unused blocks in its ration. This paper shows that rationing provides both full protection and full utilization of the cache. In addition, the same hardware support can enable energy-efficient caching and hardware-software collaborative caching. The University of Rochester Computer Science Department supported this work.