[Omp] OpenMP with different compilers

[Xiao Dong]

Thanks for all your response!

I tried the 'dplace' on our system, it did not improve the speed-up
though.  We had almost perfect speed-up before with ifort, for coarse
grained parallelization.  This time it confuses me very much with the
fine grained parallelization.



On Apr 2, 2005 5:46 PM, dkouroun at cc.uoi.gr <dkouroun at cc.uoi.gr> wrote:
> Quoting Xiao Dong <xxd104 at gmail.com>:
> 
> > Good day,
> >
> > I've been working on a Monte Carlo code paralleled with OpenMP.
> > Compiling it with pgf90 simply gives a vergy good speed up of 2.0 on
> > dual processor AMD Opteron server; compiling it with xlf90_r somehow
> > gives a speed up of 1.3 on dual processor G5 server; while compiling
> > it with ifort, the worst thing happens - the speed up is 0.5 running
> > with 2 threads on SGI Altix (8-Itanium2).  What could be the problem?
> > Supposedly, I've set the right environments on the Altix
> >
> > KMP_STACKSIZE=1g
> > OMP_DYNAMIC=FALSE
> > KMP_LIBRARY=turnaround
> > OMP_NUM_THREADS=2
> >
> >
> > Tnanks for your comments!
> >
> > Regards,
> 
> We did the same as you!
> We parallelized a Monte Carlo code using different compilers on a Quad Opteron!
> pgf77 gave a spead up up to 3.5, 3.7 on 4 CPUs. ifort was completely
> a wrong choice. Trying to run the code sequentially for example you can see
> that the best optimizations are performed by g77. g77 has the best run-time
> performance. pgf77 when trying to run sequentially gives a run-time performance
> very close to g77 (only 10-15% slower). Intels- ifort is 3-4 times slower than
> g77. About its paralle performance doesn't worth trying!
> On the contrary intel-icc C-C++ compiler is much more efficient than
> anything I know except maybe than pathscale pathCC compiler.
> 
> You should also try pathscale compilers.
> 
> And never again should you use ifort! I do not know why intel hasn't improved
> it as much as they have improved icc.
> 
> Consider also of switching to C/C++. Another world and you will enjoy it!
> That's a promise!
> 
> Best Regards!
> Drosos.
> 
>