A Novel High-Speed Memory Organization for Fine-Grain Multi-Thread Computing

Abstract

In this paper, we propose a novel organization of high-speed memories, known as the register-cache, for a multi-threaded architecture. As the term suggests, it is organized both as a register file and a cache. Viewed from the execution unit, its contents are addressable similar to ordinary CPU registers using relatively short addresses. From the main memory perspective, it is content addressable, i.e., its contents are tagged just as in conventional caches. The register allocation for the register-cache is adaptively performed at runtime, resulting in a dynamically allocated register file.

A program is compiled into a number of instruction threads called super-actors. A super-actor becomes ready for execution only when its input data are physically residing in the register-cache and space is reserved in the register-cache to store its result. Therefore, the execution unit will never stall or ‘freeze’ when accessing instruction or data. Another advantage is that since registers are dynamically assigned at runtime, register allocation difficulties at compile-time, e.g., allocating registers for subscripted variables of large arrays, can be avoided. Architectural support for overlapping executions of super-actors and main memory operations are provided so that the available concurrency in the underlying machine can be better utilized. The preliminary simulation results seem to be very encouraging: with software pipelined loops, a register-cache of moderate size can keep the execution unit usefully busy.