[Openmp-dev] Performance slowdown

[César via Openmp-dev]

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.
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