[Llvm-bgq-discuss] Status of OpenMP support in BG/Q

[Jeff Hammond]

In general, ALCF finds that -O5 is not worthwhile and often worse than
-O3.  The only exceptions of which we are aware are when the user has
tuned the code to an extreme degree - e.g. manual unrolling, blocking
for cache, vector intrinsics.

I would strongly encourage you to let IBM know that you're abandoning
it due to their lack of C++11 support.  It is important for them to
understand that their development model for XLC on Blue Gene harms
users in significant ways.

Jeff

On Thu, Feb 6, 2014 at 9:55 AM, Schlottke, Michael
<m.schlottke at fz-juelich.de> wrote:
> Hi Hal,
>
> Since the clang-omp team announced support for Clang 3.4 today I was
> wondering what the status is of OpenMP support for clang on BGQ? Are there
> any efforts going in this direction? And if not, is it due to a lack of
> interest or because it is too difficult/time consuming to do?
>
> I am asking since we finished some performance tests of mpixlcxx vs
> mpiclang++ on the BGQ in Jülich and found that even with -O5 for the XL
> compiler, the single-core runtime of the clang-compiled executables is
> usually only less than 5% higher. We are therefore thinking about dropping
> support for IBM's XL entirely, since it's the only compiler holding us back
> from C++11.
>
> Regards,
>
> Michael
>
> P. S. : If anyone is interested in the above-mentioned numbers, please let
> me know.
>
>
>
>
> ------------------------------------------------------------------------------------------------
> ------------------------------------------------------------------------------------------------
> Forschungszentrum Juelich GmbH
> 52425 Juelich
> Sitz der Gesellschaft: Juelich
> Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498
> Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher
> Geschaeftsfuehrung: Prof. Dr. Achim Bachem (Vorsitzender),
> Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt,
> Prof. Dr. Sebastian M. Schmidt
> ------------------------------------------------------------------------------------------------
> ------------------------------------------------------------------------------------------------
>
>
> _______________________________________________
> llvm-bgq-discuss mailing list
> llvm-bgq-discuss at lists.alcf.anl.gov
> https://lists.alcf.anl.gov/mailman/listinfo/llvm-bgq-discuss
>



-- 
Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at anl.gov / jhammond at uchicago.edu / (630) 252-5381
http://www.linkedin.com/in/jeffhammond
https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond