CAP: Criticality Analysis for Power-Efficient Speculative Multithreading ∗

While Speculative Multithreading (SM) on a Chip Multiprocessor (CMP) has the ability to speed-up hard-toparallelize applications, the power inefficiency of aggressive speculation is a concern. To improve SM’s power efficiency, we note that not all the tasks that are running in a SM environment are equally critical. To leverage this insight, this paper develops a novel, widely-applicable task-criticality model for SM. It also proposes CAP, a novel architecture that builds a task-criticality graph dynamically and uses it to make scheduling decisions in a SM CMP. Experiments with SPECint, SPECfp, and Olden applications show that, in a CMP with one fast core and three slow ones, the E × D 2 with CAP is, on average, 91–95 % of that without. Moreover, it is only 77–91 % of the E ×D 2 of a CMP with four fast cores and no CAP. Overall, we argue that scheduling for task criticality is beneficial. 1