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MPI_Wtime - Returns an elapsed time on the calling processor.
#include <mpi.h>
double MPI_Wtime()
INCLUDE ’mpif.h’
DOUBLE PRECISION MPI_WTIME()
#include <mpi.h>
double MPI::Wtime()
Time in seconds since an arbitrary time in the past.
MPI_Wtime
returns a floating-point number of seconds, representing elapsed wall-clock
time since some time in the past.
The "time in the past" is guaranteed
not to change during the life of the process. The user is responsible for
converting large numbers of seconds to other units if they are preferred.
This function is portable (it returns seconds, not "ticks"), it allows
high resolution, and carries no unnecessary baggage. One would use it like
this:
{
double starttime, endtime;
starttime = MPI_Wtime();
.... stuff to be timed ...
endtime = MPI_Wtime();
printf("That took %f seconds\n",endtime-starttime);
}
The times returned are local to the node that called them. There is no requirement
that different nodes return the "same" time.
The boolean variable
MPI_WTIME_IS_GLOBAL, a predefined attribute key that indicates whether
clocks are synchronized, does not have a valid value in Open MPI, as the
clocks are not guaranteed to be synchronized.
This function is intended
to be a high-resolution, elapsed (or wall) clock. See MPI_Wtick to determine
the resolution of MPI_Wtime.
On POSIX platforms, this function may utilize
a timer that is cheaper to invoke than the gettimeofday() system call,
but will fall back to gettimeofday() if a cheap high-resolution timer is
not available. The ompi_info command can be consulted to see if Open MPI
supports a native high-resolution timer on your platform; see the value
for "MPI_WTIME support" (or "options:mpi-wtime" when viewing the parsable
output). If this value is "native", a method that is likely to be cheaper
than gettimeofday() will be used to obtain the time when MPI_Wtime is invoked.
This function does not return an error value. Consequently, the result of
calling it before MPI_Init or after MPI_Finalize is undefined.
MPI_Wtick
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