| Re: [eigen] Bug in matrix product with OpenMP? |
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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] Bug in matrix product with OpenMP?
- From: Gael Guennebaud <gael.guennebaud@xxxxxxxxx>
- Date: Wed, 3 Nov 2010 16:10:28 +0100
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problem solved.
gael
2010/11/2 Björn Piltz <bjornpiltz@xxxxxxxxxxxxxx>:
> L1 cache size = 32 KB
>
> L2/L3 cache size = 3072 KB
>
> Register blocking = 8 x 4
>
> And it doesn't seem to be a problem with multi-threading per se, since I can
> comment out the #pragma omp parallel in "Parallelizer.h" and the problem
> persists. So it seems to bee the scheduling.
>
> Thanks for taking the time!
>
> 2010/11/2 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>
>>
>> sorry but I cannot reproduce on my core2 duo, gcc 4.5.0, I've also
>> added the following line:
>>
>> std::cerr << (c-d).cwiseAbs().maxCoeff() << "\n";
>>
>> and I got 0.
>>
>> Could you add the following lines at the beginning of your main() :
>>
>> std::ptrdiff_t l1 = internal::queryL1CacheSize();
>> std::ptrdiff_t l2 = internal::queryTopLevelCacheSize();
>> std::cout << "L1 cache size = " << (l1>0 ? l1/1024 : -1) << " KB\n";
>> std::cout << "L2/L3 cache size = " << (l2>0 ? l2/1024 : -1) << " KB\n";
>> typedef internal::gebp_traits<float,float> Traits;
>> std::cout << "Register blocking = " << Traits::mr << " x " <<
>> Traits::nr << "\n";
>>
>> and paste the result, please.
>>
>>
>> gael
>>
>> 2010/11/2 Björn Piltz <bjornpiltz@xxxxxxxxxxxxxx>:
>> > Hi all,
>> > I think I just ran into a bug with matrix product and OpenMP. I'm on a
>> > MacBook with GCC 4.5.1 and using latest eigen r3481:cb8a3bc8c32b (tip)..
>> > The following code fails. Seems like the last half row is filled with
>> > garbage.
>> >
>> > #include <Eigen/Core>
>> >
>> > #include <omp.h>
>> >
>> > #include <iostream>
>> >
>> > using namespace Eigen;
>> >
>> > int main(int argc, char*argv[])
>> >
>> > {
>> >
>> > int size = 1529;//Good:1528, Bad:1529
>> >
>> > MatrixXf a = MatrixXf::Random(size, size);
>> >
>> > MatrixXf b = MatrixXf::Random(size, size);
>> >
>> > omp_set_num_threads(1);
>> >
>> > MatrixXf c = a*b;
>> >
>> > omp_set_num_threads(2);
>> >
>> > MatrixXf d = a*b;
>> >
>> > if(!c.isApprox(d))
>> >
>> > std::cerr<<size<<" Error!"<<std::endl;
>> >
>> > return 0;
>> >
>> > }
>> >
>> > g++ -I /path/to/eigen -fopenmp -O3 -DNDEBUG product_bug.cpp -o
>> > product_bug
>> >
>>
>>
>
>