Clock Synchronization

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Clock Synchronization

clock synchronization The value returned for MPI_WTIME_IS_GLOBAL is 1 if clocks MPI_WTIME_IS_GLOBAL at all processes in MPI_COMM_WORLD are synchronized, 0 otherwise. A collection of clocks is considered synchronized if explicit effort has been taken to synchronize them. The expectation is that the variation in time, as measured by calls to MPI_WTIME, will be less then one half the round-trip time for an MPI message of length zero. If time is measured at a process just before a send and at another process just after a matching receive, the second time should be always higher than the first one.

The attribute MPI_WTIME_IS_GLOBAL need not be present when MPI_WTIME_IS_GLOBAL the clocks are not synchronized (however, the attribute key MPI_WTIME_IS_GLOBAL is always valid). This attribute may be associated with communicators other then MPI_COMM_WORLD.

The attribute MPI_WTIME_IS_GLOBAL has the same value on all processes in the group of MPI_COMM_WORLD.

 MPI_GET_PROCESSOR_NAME(name, resultlen)
    OUT       name        A unique specifier for the current
                          physical node.
    OUT       resultlen   Length(in printable characters) of the
                          result returned in name 
MPI_Get_processor_name(char *name, int *resultlen)


This routine returns the name of the processor on which it was called at the moment of the call. The name is a character string for maximum flexibility. From this value it must be possible to identify a specific piece of hardware; possible values include ``processor 9 in rack 4 of'' and ``231'' (where 231 is the actual processor number in the running homogeneous system). The argument name must represent storage that is at least MPI_MAX_PROCESSOR_NAME characters long. MPI_MAX_PROCESSOR_NAME MPI_GET_PROCESSOR_NAME may write up to this many characters into name.

The number of characters actually written is returned in the output argument, resultlen.

The constant MPI_BSEND_OVERHEAD provides an upper bound on MPI_BSEND_OVERHEAD the fixed overhead per message buffered by a call to MPI_BSEND.

Jack Dongarra
Fri Sep 1 06:16:55 EDT 1995