On Task Relocation in Two-Dimensional Meshes

In parallel computer systems with a number of processors, external fragmentation is caused by continuous allocation and deallocation of processors to tasks which require exclusive use of several contiguous processors. With this condition, the system may not be able to find contiguous processors to be allocated to an incoming task even with a sufficient number of free processors. Relocation is an approach for alleviating this problem by reassigning the running tasks to other processors. In this paper, we examine two relocation schemes full relocation and partial relocation scheme for two-dimensional meshes. The full relocation scheme is desirable when the system is highly fragmented, while the partial relocation scheme is used for minimizing the number of relocated tasks. For the relocation process, we formally define and use two basic submesh movement operations shifting and rotating. Comprehensive computer simulation reveals that the proposed schemes are beneficial when the relocation overhead is not high, which is machine dependent. 2000 Academic Press