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Subject: [OMPI users] Interaction between Intel and OpenMPI floating point exceptions
From: Steve Lowder (lowder_at_[hidden])
Date: 2009-04-06 19:22:55


Recently I've been running an MPI code that uses the LAPACK slamch
routine to determine machine precision parameters. This software is
compiled using the latest Intel Fortran compiler and setting the -fpe0
argument to watch for certain floating point errors. The slamch
routines crashed and printed an OpenMPI stacktrace to report an
underflow error, however the Intel -fpe0 setting doesn't abort on
underflow. When this software is not compiled and linked with OpenMPI,
it ignores the underflow and doesn't abort when compiled with -fpe0.

When I run the MPI version and set --mca opal_signal 6,7,11 the code
doesn't abort on underflow. I'd like to know if I'm interpreting this
behavior correctly, it appears that the mpi versus no mpi cases handle
underflow differently. I'm assuming OpenMPI has a handler that processes
the interrupts ahead of the Fortran RTL, stopping execution. Otherwise
the Fortran RTL handler would just ignore the underflow. Do I sort of
understand what is going on here? Is there another solution short of
the --mca opal_signal switch?

thanks
Steve