[Beowulf] Re:Strange hardware? problems

Orion Poplawski orion at cora.nwra.com
Tue May 1 14:41:28 PDT 2007

David Mathog wrote:
> Since the same code runs differently on two different Opteron models
> it's probably either a memory access issue or the use of a compiler
> flag that enables some feature on one model that is not present
> on the other.  For instance, SSE3 vs. SSE2, although I don't know
> enough about these models to tell you what the most likely flag would
> be.  (The fact that it runs ok on the newer one and blows up on the
> older one is consistent with this type of error.)
> Assuming gcc, recompile with:
>   -O0 -g -std=c99 -Wall
> and clean up any warnings that result until you get a clean build.
> Repeat with -O3 and -O2, as for strange reasons that sometimes uncovers
> logic problems not seen at -O0.  Then run the resulting binary
> within valgrind.  Fix any memory access violations which are found.
> Valgrind can also alert you to the use of unsupported operations.

The code compiles quite cleanly, but I am seeing different behavior with 
  different compiler flags and different compilers.  We'll see if I can 
bisect the problem into a small enough box.

Thanks for the poke in that direction...

Orion Poplawski
Technical Manager                     303-415-9701 x222
NWRA/CoRA Division                    FAX: 303-415-9702
3380 Mitchell Lane                  orion at cora.nwra.com
Boulder, CO 80301              http://www.cora.nwra.com

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