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Ublas : |
From: Tan, Sarah \(FID\) (Sarah.Tan_at_[hidden])
Date: 2007-09-24 10:02:09
Hi
I am wondering whether anyone has experience with the stability issue
when compiling ublas with Intel C++ Compiler for Windows (ICC 9.1).
Problem arises when parallel code is generated (boost library 1.33.1).
The parallelization scheme is quite simple. There are four threads for a
four-core machine. Each thread dumps output to a ublas matrix. They then
got accumulated into a final matrix when four threads all come back.
ublas::matrix<double> output(n1, n2);
output.clear();
std::vector< ublas::matrix<double> > outputVec;
for (unsigned i = 0; i < 4; ++i)
{
ublas::matrix<double> um(n1, n2);
um.clear();
outputVec.push_back(um);
}
#pragma omp parallel
{
#pragma omp sections
{
#pragma omp section
{ outputVec[0] = doSomething();}
#pragma omp section
{ outputVec[1] = doSomething();}
#pragma omp section
{ outputVec[2] = doSomething();}
#pragma omp section
{ outputVec[3] = doSomething();}
}
#pragma omp barrier
for (unsigned i = 0; i < 4; ++i)
output += outputVec[i];
If ICC "Generate parallel code /QOpenmp" option is selected, output is
unstable. If ICC "Generate sequential code /QOpenmp-stubs" option is
selected, output is STABLE, but of course I no longer enjoy the speed
boost because omp directives are ignored.
The whole parallelization scheme is perfectly stable if std::vector
based matrix is used rather than ublas, which is considerably slower
than ublas.
How can I get a stable paralyzed ublas-based implementation? Any input
is much appreciated.
Thanks
Sarah
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