Cache Coherence Protocol Design for Active Memory Systems

Abstract — Active memory systems improve application cache behavior by either performing data parallel computation in the memory elements or supporting address re-mapping in a specialized memory controller. The former approach allows more than one memory element to operate on the same data, while the latter allows the processor to access the same data via more than one address— therefore data coherence is essential for correctness and transparency in active memory systems. In this paper we show that it is possible to extend a conventional DSM coherence protocol to handle this problem efficiently and transparently on uniprocessor as well as multiprocessor active memory systems. With a specialized programmable memory controller we can support several active memory operations with simple coherence protocol code modifications, and no hardware changes. This paper presents details of the DSM cache coherence protocol extensions that allow speedup from 1.3 to 7.6 over normal memory systems on a range of simulated uniprocessor and multiprocessor active memory applications.