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Make OpenBLAS's usage of OpenMP respect openblas_set_num_threads() #5808

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Merged
martin-frbg merged 1 commit into from
Jul 13, 2026
+14 −4
Merged

Make OpenBLAS's usage of OpenMP respect openblas_set_num_threads() #5808

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9 changes: 9 additions & 0 deletions common_thread.h
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Original file line number Diff line number Diff line change
Expand Up @@ -138,10 +138,19 @@ typedef struct blas_queue {
extern int blas_server_avail;
extern int blas_omp_number_max;
extern int blas_omp_threads_local;
extern int blas_is_num_threads_set_explicitly;

static __inline int num_cpu_avail(int level) {

#ifdef USE_OPENMP
/* If the user explicitly called openblas_set_num_threads(),
respect that setting instead of overriding it with
`omp_get_max_threads()` below (which is to get a default
in case the user hasn't made an explicit choice). */
if (blas_is_num_threads_set_explicitly) {
return blas_cpu_number;
}

int openmp_nthreads;
openmp_nthreads=omp_get_max_threads();
if (omp_in_parallel()) openmp_nthreads = blas_omp_threads_local;
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9 changes: 5 additions & 4 deletions driver/others/blas_server_omp.c
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Expand Up @@ -70,6 +70,7 @@
int blas_server_avail = 0;
int blas_omp_number_max = 0;
int blas_omp_threads_local = 1;
int blas_is_num_threads_set_explicitly = 0; // tracks whether the user called openblas_set_num_threads()

extern int openblas_omp_adaptive_env(void);

Expand Down Expand Up @@ -122,7 +123,7 @@ void goto_set_num_threads(int num_threads) {

}
void openblas_set_num_threads(int num_threads) {

blas_is_num_threads_set_explicitly = 1;
goto_set_num_threads(num_threads);
}

Expand All @@ -145,7 +146,7 @@ extern int openblas_omp_num_threads_env(void);

if(blas_omp_number_max <= 0)
blas_omp_number_max= openblas_omp_num_threads_env();
if (blas_omp_number_max <= 0)
if (blas_omp_number_max <= 0)
blas_omp_number_max=MAX_CPU_NUMBER;
#else
blas_omp_number_max = omp_get_max_threads();
Expand Down Expand Up @@ -365,14 +366,14 @@ static void exec_threads(int thread_num, blas_queue_t *queue, int buf_index){
#ifdef BUILD_COMPLEX16
sb = (void *)(((BLASLONG)sa + ((ZGEMM_P * ZGEMM_Q * 2 * sizeof(double)
+ GEMM_ALIGN) & ~GEMM_ALIGN)) + GEMM_OFFSET_B);
#else
#else
fprintf(stderr,"UNHANDLED COMPLEX16\n");
#endif
} else if ((queue -> mode & BLAS_PREC) == BLAS_SINGLE) {
#ifdef BUILD_COMPLEX
sb = (void *)(((BLASLONG)sa + ((CGEMM_P * CGEMM_Q * 2 * sizeof(float)
+ GEMM_ALIGN) & ~GEMM_ALIGN)) + GEMM_OFFSET_B);
#else
#else
fprintf(stderr,"UNHANDLED COMPLEX\n");
#endif
} else {
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