[Openmp-dev] Performance slowdown

[via Openmp-dev]

César,

> - The version of Clang that I am using to compile the benchmarks: 3.5.0

Clang 3.5 doesn't support OpenMP -- it simply ignores the pragmas.

Please use version from trunk or from 3_7 release branch. Also, please supply -fopenmp= libomp option.

Yours,
Andrey Bokhanko
=============
Software Engineer
Intel Compiler Team
Intel

Отправлено с iPad

> 18 авг. 2015 г., в 21:14, César via Openmp-dev <openmp-dev at lists.llvm.org> написал(а):
> 
> Hello,
> 
> I don't know if this is the correct list to talk about this - I did not find a better place..
> 
> I am doing performance experiments with a few OpenMP implementations (IOMP, GOMP and our private impl.) and I am seeing a severe slowdown when I use IOMP (GOMP and others are performing well). 
> 
> The benchmarks I am using are these ones: http://kastors.gforge.inria.fr/#!index.md
> 
> Really, the slowdown is huge. For one of the programs (plasma/dpotrf_taskdep -n 8192 -b 64 -i 1 -c) the serial version executes in ~28s and the parallel one executes in ~110s. I did some profiling and found that most of the time is being spent on synchronization barriers and dependence tracking (see attached image). Before digging deeper I would like to hear back from you if I am doing something wrong here:
> 
> - I tested with the last version of the repository:  http://llvm.org/svn/llvm-project/openmp/trunk
> - I am using Ubuntu 14.10.
> - I have tested on more than one machine, the results above are from a Intel i7-3770
> - The runtime itself is compiled using: make compiler=gcc os_omp=linux arch=32e
> - The version of GCC that I am using is: 4.9.1
> - The version of Clang that I am using to compile the benchmarks: 3.5.0
> 
> 
> César.
> <pic1.png>
> <pic2.png>
> <pic3.png>
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