The Effect of Communication and Synchronization on Amdahl Law in Multicore Systems

This work analyses the effects of sequential-to-parallel synchronization and inter-core communication on multicore performance, speedup and scaling. A modification of Amdahl law is formulated, to reflect the finding that parallel speedup is lower than originally predicted, due to these effects. In applications with high inter-core communication requirements, the workload should be executed on a small number of cores, and applications of high sequential-to-parallel synchronization requirements may better be executed by the sequential core, even when f, the Amdahl fraction of parallelization, is very close to 1. To improve the scalability and performance speedup of a multicore, it is as important to address the synchronization and connectivity intensities of parallel algorithms as their parallelization factor.