User and Reference Guide

Contents

MPI_Wtime()

This timer is provided by the MPI implementation. In general this is simply a wrapper around
gettimeofday()
and then using it instead of
gettimeofday()
only has disadvantages: with
gettimeofday()
Intel® Trace Collector knows that processes running on the same node share the same clock and thus does not synchronize between them. The same information cannot be obtained through the MPI API and thus Intel® Trace Collector is conservative and assumes that clock synchronization is needed. This can be overridden with the
SYNCED-HOST
configuration option. Another disadvantage is increased overhead and potentially implementation errors in MPI.
If the MPI has access to a better timer source (for example a global clock in the underlying communication hardware), then using this timer would be advantageous.

Product and Performance Information

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Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.