Opteron Fortran (was Re: flood of bounces frompostmaster at systemsfirm.net)

Brian Dobbins brian.dobbins at yale.edu
Wed Oct 22 09:38:00 EDT 2003


> PGI's first AMD64 production release was around July 5.  There is a 
> limitation on objects greater than 2GB in Linux as a result of the GNU 
> assembly linker, but the application can address as much memory as you 

  One simple way to get around the 2GB limit (*) is to simply use FORTRAN 
90 dynamic allocation calls - we've done this, and have run codes up to 
(so far) about 7.7GB in size.  If you're used to static allocations in 
F77, it's only about two lines to alter things to use dynamic mem.

  (*) - I don't think this limitation is in the GNU assembly linker, since 
g77 has no problems here.  I think if you compile to assembly, you'll see 
that PGI has issues with 32-bit wraparound, whereas g77 does not.  Their 
tech people are aware of this, and it's something I expect will be fixed 
farily soon.

  Also, if you do happen to run jobs > 4GB, make sure you update the 'top' 
version you're using (procps.sourceforge.net).  Previous versions had 
wraparound at the 4GB mark, and it's cool seeing a listing say something 
to the effect of "7.7G" next to the size.  :)

  Cheers,
  - Brian

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