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Ublas : |
From: Riccardo Rossi (rrossi_at_[hidden])
Date: 2007-09-25 02:28:09
Hi Sarah,
i have little experience with OpenMP nevertheless i am really interested
in the subject.
there are two things in your code that i find a little strange:
1 - you do "um.clear();" before pushing back... i guess with this you
may be breaking the memory as you will be adding a 0*0 matrix while
later you may suppose it is different from zero.
2 - this is NOT an error but... why are u using sections?
greetings
Riccardo
Tan, Sarah (FID) wrote:
> 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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