Design choices for the TOP-1 multiprocessor workstation

A snoopy-cache-based multiprocessor workstation called TOP-1 (TOkyo research Parallel processor-1) was developed to evaluate multiprocessor architecture design choices as well as to conduct research on operating systems, compilers, and applications for multiprocessor workstations. TOP-1 is a ten-way multiprocessor using the Intel 80386™ microprocessor chip and the Weitek WTL 1167™ floating-point coprocessor chip. It is currently running under a multiprocessor version of AIX® , which was also developed at the IBM Tokyo Research Laboratory. Our research interest was focused on the design of an effective snoopy cache (all caches monitor all memory-cache traffic) system and the quantitative evaluation of its performance. One of the unique aspects of the TOP-1 design is that the cache supports four different, original snoopy protocols, which may coexist in the system. To evaluate the performance, we implemented a hardware statistics monitor that gathers statistical data. This paper focuses mainly on the TOP-1 cache design—its protocol, and its evaluation by means of the statistics monitor. Besides its cache design, TOP-1 has three other unique architectural features: two independently arbitrated 64-bit buses supported by two snoopy-cache controllers per processor, a communication and interruption mechanism for notifying other processors of asynchronous events, and an efficient arbitration mechanism to allow prioritized quasi-round-robin service with distributed control. These features are also described in detail.