The effect of communication and synchronization on Amdahl’s law in multicore systems

• Effects of sequential-to-parallel synchronization on multicore performance analyzed.
• Effects of inter-core communication on multicore performance analyzed.
• A number of performance models are compared.
• A modification of Amdahl’s law is formulated.

This work analyses the effects of sequential-to-parallel synchronization and inter-core communication on multicore performance, speedup and scaling from Amdahl’s law perspective. Analytical modeling supported by simulation leads to a modification of Amdahl’s law, reflecting lower than originally predicted speedup, due to these effects. In applications with high degree of data sharing, leading to intense inter-core connectivity requirements, the workload should be executed on a smaller number of larger cores. Applications requiring intense sequential-to-parallel synchronization, even highly parallelizable ones, may better be executed by the sequential core. 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.