PRISM: an integrated architecture for scalable shared memory

This paper describes PRISM, a distributed shared memory architecture that relies on a tightly integrated hardware and operating system design for scalable and reliable performance. PRISM's hardware provides mechanisms for flexible management and dynamic configuration of shared memory pages with different behaviors. As an example, PRISM can configure individual shared memory pages in both CC-NUMA and Simple-COMA styles, maintaining the advantages of both without incorporating any of their disadvantages. PRISM's operating system is structured as multiple independent kernels, where each kernel manages the resources on its local node. PRISM's system structure minimizes the amount of global coordination when managing shared memory. Page faults do not involve global TLB invalidates, and pages can be replicated and migrated without requiring global coordination. The structure also provides natural fault containment boundaries around each node because physical addresses do not address remote memory directly. We simulate PRISM's hardware, cache coherence protocol and memory management algorithms. Results from SPLASH applications on the simulated machine demonstrate a tradeoff between CC-NUMA and Simple-COMA styles of memory management. Adaptive, run-time policies that take advantage of PRISM's ability to dynamically configure shared memory pages with different behaviors significantly outperform pure CC-NUMA or Simple-COMA configurations and are usually within 10% of optimal performance.