LitTLS: Lightweight Thread-Level Speculation on Little Cores

Thread-Level Speculation (TLS) utilizes speculative parallelization to accelerate hard-to-parallelize serial codes on multi-cores. As the heterogeneous multi-core architecture is becoming ubiquitous, it presents an opportunity for TLS to reorganize little cores for the acceleration of these serial codes instead of a big core with similar or more area and power. However, previous TLS designs significantly suffer from extended hardware overhead and costly speculative forwarding. We present LitTLS, a lightweight TLS design with versioning caches to eliminate significant extended hardware overhead by storing versions in caches without speculative write buffers and memory undo-logs. Additionally, LitTLS introduces the Speculative Address Table, a novel component to accelerate speculative forwarding with a central structure to trace memory dependencies. Evaluations on four little cores show that LitTLS achieves an average performance speedup of 2.87× compared to a little core, outperforming a big core by 94% with similar area and less power. The extended area size is only 0.07 mm 2 , and the maximum increase in dynamic power consumption is limited to 0.3%, compared to four little cores.