Application-bypass reduction for large-scale clusters
by Adam Wagner, Darius Buntinas, Ron Brightwell, Dhabaleswar K. Panda
International Journal of High Performance Computing and Networking (IJHPCN), Vol. 2, No. 2/3/4, 2004

Abstract: Process skew is an important factor in the performance of parallel applications, especially in large-scale clusters. Reduction is a common collective operation which, by its nature, introduces implicit synchronisation between the processes involved in the communication and is therefore highly susceptible to performance degradation due to process skew. A collective operation with application-bypass does not require the application to block in order for the operation to make progress. Application-bypass collective operations are therefore highly tolerant of skew. In this paper, we describe the design and implementation of an application-bypass version of the reduction operation in MPICH over GM. We evaluate our implementation on a 32-node cluster. Under conditions of process skew we find a factor of improvement of up to 5.1 for our application-bypass reduction versus the default MPICH implementation. In addition, we see that this factor of improvement increases with system size, indicating that the application-bypass implementation is more scalable and skew-tolerant than the default non-application-bypass version. This framework promises design and development of high-performance and scalable collective communication libraries for next-generation large-scale clusters.

Online publication date: Thu, 02-Feb-2006

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