Speculative Execution for Hiding Memory Latency

摘要

L2 misses are one of the main causes for stalling the activity in current and future microprocessors. In this paper we present a mechanism to speculatively execute independent instructions of L2-miss loads, even if no entry in the reorder buffer is available. The proposed mechanism generates future instances of instructions that are expected to be independent of the delinquent load. When these dynamic instructions are later fetched, they use the previously precomputed data and directly go to the commit stage without executing. The mechanism replicates strided loads found above the L2-miss load, that produce the data for the target independent instructions. Instructions following the L2-miss load will check if their source operands have been replicated. In this case, multiple speculative instances of them will also be generated. This mechanism is built on top of a superscalar processor with an aggressive prefetch scheme. Compared to this baseline, the mechanism obtains 21% of performance improvement.