On May 6, 2012, at 12:19 PM, Jed Brown wrote: > On Sun, May 6, 2012 at 11:07 AM, Barry Smith <bsmith at mcs.anl.gov> wrote: > Is your specific questions is: should we replace all MPI_Init() calls in > PETSc with MPI_Init_thread(...,MPI_THREAD_FUNNELED,...)? > > Can't do this because of MPI-1 compatibility, but yeah, I'm thinking of > always using MPI_THREAD_FUNNELED if configure picks it up. > > > Will there be a performance hit, when one is not using threads? Should we > #if defined() do the replacement if the user has turned on OpenMP or Pthread > or TBB only and not by default? > > Sounds like there is not likely to be a performance hit because the standard > system routines are thread safe. > > http://lists.mcs.anl.gov/pipermail/mpich-discuss/2012-May/012380.html > > MPICH2 does not use POSIX functions like getchar_unlocked() or non-POSIX > stuff like fwrite_unlocked(), so it seems like the library will be doing > exactly the same thing in both cases.
I could care less about MPICH2. What happens on the Cray if one switches, sudden 50% drop in performance? Barry
