openBLAS nested parallelism

Hi,
we are trying to run two instances of cblas_dgemm in parallel. If the total number of threads is 16, we would like each instance to run using 8 threads. Currently, we are using a structure like this:
#pragma omp parallel num_threads(2)
{
if (omp_get_thread_num() == 0){
cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans,
bs1, bs2, bs3, alpha, pTmpA, bs3, pTmpB, bs2, beta, pTmpC, bs2);
}else {
cblas_dgemm(CblasRowMajor, CblasNoTrans, CblasNoTrans,
bs1, bs2, bs3, alpha, pTmpA2, bs3, pTmpB2, bs2, beta, pTmpC2, bs2);
}
}
Here is the issue:

• At the top level, there are two OpenMP threads each of which is active inside one of the if/else blocks. Now, we expect those threads to call the cblas_dgemm functions is parallel, and inside those cblas_dgemm functions, we expect new threads to be spawned.

• To set the number of threads internal to each cblas_dgemm, we set the corresponding environment variable: setenv OPENBLAS_NUM_THREADS 8
  However, it doesn't seem to be working. If we measure the runtime for each of the parallel calls, the runtime values are equal, but they are equal to the runtime of a single cblas_dgemm call when nested parallelism is not used and the environment variable OPENBLAS_NUM_THREADS is set to 1.

What is going wrong? and how can we have the desired behavior?
Is there any way we could know the number of threads inside the cblas_dgemm function?

Thank you very much for your time and help

Inizia con il wrapper OpenMP segnalato attorno a cblas_dgemm e l’impostazione OPENBLAS_NUM_THREADS, quindi esamina la documentazione sul threading di OpenBLAS e l’implementazione di cblas_dgemm. Determina se sono supportate chiamate parallele annidate e come sia possibile osservare il numero dei relativi worker. Il lavoro è completato quando viene fornita una configurazione verificata oppure vengono documentati il limite e il comportamento supportato.