On Sat, Jul 17, 2010 at 09:14:11AM -0700, Eugene Loh wrote: > Jeff Squyres wrote: > > >On Jul 17, 2010, at 4:22 AM, Anton Shterenlikht wrote: > > > > > >>Is loop vectorisation/unrolling safe for MPI logic? > >>I presume it is, but are there situations where > >>loop vectorisation could e.g. violate the order > >>of execution of MPI calls? > >> > >> > >I *assume* that the intel compiler will not unroll loops that contain MPI > >function calls. That's obviously an assumption, but I would think that > >unless you put some pragmas in there that tell the compiler that it's safe > >to unroll, the compiler will be somewhat conservative about what it > >automatically unrolls. > > > > > More generally, a Fortran compiler that optimizes aggressively could > "break" MPI code. > > http://www.mpi-forum.org/docs/mpi-20-html/node236.htm#Node241 > > That said, you may not need to worry about this in your particular case.
This is a very important point, many thanks Eugene. Fortran MPI programmer definitely needs to pay attention to this. MPI-2.2 provides a slightly updated version of this guide: http://www.mpi-forum.org/docs/mpi22-report/node343.htm#Node348 many thanks anton -- Anton Shterenlikht Room 2.6, Queen's Building Mech Eng Dept Bristol University University Walk, Bristol BS8 1TR, UK Tel: +44 (0)117 331 5944 Fax: +44 (0)117 929 4423
