Characterizing the Performance and Energy Efficiency of Simultaneous Multithreading in Multicore Environments

In the context of the rapid slowing of Dennard´s scaling, we characterize the efficacy of one of the power-management mechanisms, namely concurrency throttling, which adapts the concurrency (i.e., number of active threads per core) of an application via simultaneous multithreading (SMT). SMT can potentially improve the processor utilization and thus the efficiency of the processor for parallel programs by filling-in the unused issue slots and hiding memory latency on wide-issue super scalar architectures. However, the benefit of using concurrency throttling is highly dependent on the workload. Moreover, previous work in this area occurred on microprocessor platforms where the slowdown effect of Dennard´s scaling had yet to have significant effect, thus providing the motivation for our work: understanding the efficacy of SMT on a modern multicore platform.