Dynamic Characteristics of Multithreaded Execution in the EM - X Multiprocessor

Multithreading is known be e ective for tolerating communication latency in distributed-memory multiprocessors. Two types of support for multithreading have been used to date including software and hardware. This paper presents the impact of multithreading on performance through empirical studies. In particular, we explicate the performance di erence between software support and hardware support for the 80-processor EM-X distributed-memory multiprocessor which we have designed and implemented. The EMX provides three types of hardware supports for ne-grain multithreading including direct remote memory access, fast thread invocation, and dedicated instructions for generating xed-sized communication packets. To demonstrate the e ect of multithreading, we have performed various experiments using micro benchmark programs and MP3D, one of the SPLASH benchmarks. Three types of performance parameters have been measured including processor e ciency, remote memory latency, and network load. Experimental results indicate that the EM-X architecture is highly e ective for supporting the multithreading principles of execution through dedicated hardware and software. keywords Multithreading, latency hiding, ne grain communication, direct remote memory access, shared memory benchmark, synthetic workload.