Evaluation of a "Stall" Cache: An Efficient Restricted On-chip Instruction Cache

In this report we compare the cost and performance of a new kind of restricted instruction cache architecture -- the stall cache -- against several other conventional cache architectures. The stall cache minimizes the size of an on-chip instruction cache by caching only those instructions whose instruction fetch phase collides with the memory access phase of a preceding load or store instruction. Many existing machines provide a single cycle external cache memory [6, 17, 2]. Our results show that, under this assumption, the stall cache always outperforms an equivalent sized on-chip instruction cache, reducing external memory access stalls by approximately 10%. In addition we present results for a system using an onchip data cache, and for one with a double width data bus and short instruction prefetch buffer