I have written a code which performs LU-factorization with OpenMP. I feel like the code is performing too slow. The computer I am working on have 16 cores and the time for 16 threads is 12.5s and for 4 threads 14.3s. This is the section of the code where the parallelization is happening. I am new to C programming and feel like I am missing something that is slowing the multithreading down.
/*__Initialize lock__*/
omp_lock_t lock[n];
for(i=0;i<n;i++)
omp_init_lock(&lock[i]);
/*___Create theads____*/
#pragma omp parallel private(i,j,k,thread) num_threads(nThreads)
{
thread=omp_get_thread_num();
#pragma omp for schedule(static)
for(i=0;i<n;i++) omp_set_lock(&lock[i]);
if(thread==0)
omp_unset_lock(&lock[0]);
for(i=0;i<n;i++){
div=1/U[i][i];
#pragma omp for schedule(static)
for(j=i+1;j<n;j++)
L[j][i]=U[j][i]*div;
#pragma omp for schedule(static)
for(j=i+1;j<n;j++){
for(k=i;k<n;k++)
U[j][k]=U[j][k]-L[j][i]*U[i][k];
if(j==i+1)
omp_unset_lock(&lock[i+1]);
}
}
}
Based on the code that you have provided it seems to me that you do not need any lock whatsoever, try the following parallel version:
#pragma omp parallel num_threads(nThreads)
{
for(int i=0;i<n;i++){
div=1/U[i][i];
#pragma omp for schedule(static)
for(j=i+1;j<n;j++)
L[j][i]=U[j][i]*div;
#pragma omp for schedule(static)
for(int j=i+1;j<n;j++){
for(int k=i;k<n;k++)
U[j][k]=U[j][k]-L[j][i]*U[i][k];
}
}
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