Optimizing the Synchronization Operations in Message Passing Interface One-Sided Communication

  • Authors:

  • Rajeev Thakur;William Gropp;Brian Toonen

  • Affiliations:

  • Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, USA;Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, USA;Mathematics and Computer Science Division, Argonne National Laboratory, Argonne, IL 60439, USA

  • Venue:
  • International Journal of High Performance Computing Applications
  • Year:
  • 2005

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Abstract

One-sided communication in Message Passing Interface (MPI) requires the use of one of three different synchronization mechanisms, which indicate when the one-sided operation can be started and when the operation is completed. Efficient implementation of the synchronization mechanisms is critical to achieving good performance with one-sided communication. However, our performance measurements indicate that in many MPI implementations, the synchronization functions add significant overhead, resulting in one-sided communication performing much worse than point-to-point communication for short- and medium-sized messages. In this paper, we describe our efforts to minimize the overhead of synchronization in our implementation of one-sided communication in MPICH2. We describe our optimizations for all three synchronization mechanisms defined in MPI: fence, post-start-complete-wait, and lock-unlock. Our performance results demonstrate that, for short messages, MPICH2 performs six times faster than LAM for fence synchronization and 50% faster for post-start-complete-wait synchronization, and it performs more than twice as fast as Sun MPI for all three synchronization methods.