This article analyzes the influence of VM allocation policies in cloud on the latency of MPI communications. Two popular MPI collectives, Bcast and Exchange, have been analyzed over two types of infrastructures: a cloud based on Apache CloudStack, employing commodity hardware, and a non-virtualized cluster, also employing commodity hardware. The main goal of this article is analyzing the effects on the MPI latency that introduce the allocation police employed by the cloud platform to deploy the Virtual Machines. Two opposite allocation schemes have been considered: concentrated, in which the Virtual Machines are allocated in the same host, and scattered, in which the Virtual Machines are spread using different hosts. The MPI communications have been analyzed for message sizes ranging from 1 byte to 4096 KiB. The results show that the cloud layer introduces a considerable overhead in the latency of Bcast and Exchange communications. However, if the cloud is employed to execute MPI applications, the concentrated allocation scheme is suitable for messages of less than 4 KiB, whereas for larger messages the scattered allocation scheme is better.
Keywords: Virtualization, virtual machines, benchmark, cloud, cluster, MPI