Turbo-ROB: A Low Cost Checkpoint/Restore Accelerator

Abstract. Modern processors use speculative execution to improve performance. However, speculative execution requires a checkpoint/restore mechanism to repair the machine’s state whenever speculation fails. Existing checkpoint/restore mechanisms do not scale well for processors with relatively large windows (i.e., 128 or more). This work presents Turbo-ROB, a checkpoint/restore recovery accelerator that can complement or replace existing checkpoint/restore mechanisms. We show that the Turbo-ROB improves performance and reduces resource requirements compared to a conventional Re-order Buffer mechanism. For example, on the average, a 64-entry TROB matches the performance of a 512-entry ROB, while a 128- and a 512-entry TROB outperform the 512-entry ROB by 6.8 % and 9.1 % respectively. We also demonstrate that the TROB improves performance with register alias table checkpoints effectively reducing the need from more checkpoints and the latency and energy increase these would imply.