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Subject: Re: [OMPI users] Interaction between Intel and OpenMPI floating point exceptions
From: Steve Lowder (lowder_at_[hidden])
Date: 2009-04-07 19:03:35

  Thanks for the reply, yours sounds like a good suggestion to try to
work around this.

Iain Bason wrote:
> On Apr 6, 2009, at 7:22 PM, Steve Lowder wrote:
>> 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?
> Your analysis sounds about right to me. There are Fortran intrinsic
> routines that can get those machine precision parameters instead of
> slamch. Would it be feasible to modify the code to use them?
> Iain
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