[Openmp-dev] Performance slowdown

[César via Openmp-dev]

On Wed, Aug 19, 2015 at 3:07 PM, Jack Howarth <
howarth.mailing.lists at gmail.com> wrote:

> On Tue, Aug 18, 2015 at 2:14 PM, César via Openmp-dev
> <openmp-dev at lists.llvm.org> wrote:
> > 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
>
> That web page claims the benchmarks use parts of the OpenMP 4.0
> specification.
>
> "The KaStORS benchmark suite has been designed to evaluate the
> implementation of
> the OpenMP dependent task paradigm, introduced as part of the OpenMP 4.0
> specification."
>
> Currently openmp is only complete for the OpenMP 3.2 specification
>
>
I am able to compile a few benchmarks that use task dependence annotations
(from OMP 4.0) but for those that specify the range of the memory
dependence I get syntax error. So, should I assume that this part is not
implemented, right? Is there a list for the OMP 4.0 items that are
currently supported?

BTW, the Clang version from Github was able to parse these annotations, was
it dropped from the current newer version?



> >
> > 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.
> >
> > _______________________________________________
> > Openmp-dev mailing list
> > Openmp-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/openmp-dev
> >
>
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