The Effect of Speculative Execution on Cache Performance

Superscalar microprocessors obtain high performance by exploiting parallelism at the instruction level. To effectively use the instruction-level parallelism found in general purpose, non-numeric code, future processors will need to speculatively execute far beyond instruction fetch limiting conditional branches. One result of this deep speculation is an increase in the number of instruction and data memory references due to the execution of mispre-dicted paths. Using a tool we developed to generate speculative traces from Intel architecture Unix binaries, we examine the differences in cache performance between speculative and non-speculative execution models. The results pertaining to increased memory traffic, mispre-dicted path reference effects, allocation strategies, and speculative write buffers are discussed.