Process vs. task migration

This paper describes task and process migration for the OSF/1 AD Operating System (OS server for massively parallel processors and clusters of workstations. OSF/1 AD, runs in user space, on top of the Mach microkernel. A process in the OSF/1 AD server is composed of a Mach task state (memory, capabilities, threads, etc.) and of the UNIX-related state (open file descriptors, signal masks, etc.). Process migration invokes task migration to transfer the Mach task state, and supports transparent transfer of the UNIX process state. Process and task migration rely on a single system image provided at both OSF/1 AD and Mach levels. We compare the initial and run-time costs of task and process migration for several programs with different needs. While process migration initial costs are less than 17% of task migration costs, the expected benefits can easily be as high as a 50% improvement in run-time cost over task migration. We conducted the experiments on a cluster of PCs; however, results are also applicable to massively parallel processors.