Gilles Gouaillardet <gilles.gouaillar...@gmail.com> writes: > Dave, > > fwiw, on v1.10, we likely use the number of cycles / cpu freq.
That would be a horribly broken means of timing. gettimeofday is actually called under mpi_wtime, as ompi_info claims. > see opal_sys_timer_get_cycles in > https://github.com/open-mpi/ompi-release/blob/v1.10/opal/include/opal/sys/amd64/timer.h > > I cannot remember whether this is a monotonic timer. > (e.g. MPI_Wtime() invoked on a given cpu is always lower or equal to > MPI_Wtime() invoked later and on *any* cpu) That's global, not monotonic. MPI_Wtime(1) says it isn't necessarily global in OMPI, but it has to be monotonic as I understand it. > that could be the reason why we moved to clock_gettime() in master. The reason to use clock_gettime is higher precision. (I looked into this after numbers from a test didn't make much sense.)
