Accelerate framework uses only one core on Mac M1

The following C program (dgesv_ex.c)

Code Block #include <stdlib.h>#include <stdio.h>/* DGESV prototype */extern void dgesv( int* n, int* nrhs, double* a, int* lda, int* ipiv,                double* b, int* ldb, int* info );/* Main program */int main() {        /* Locals */        int n = 10000, info;        /* Local arrays */        /* Initialization */        double *a = malloc(n*n*sizeof(double));        double *b = malloc(n*n*sizeof(double));        int *ipiv = malloc(n*sizeof(int));        for (int i = 0; i < n*n; i++ )        {                a[i] = ((double) rand()) / ((double) RAND_MAX) - 0.5;        }        for(int i=0;i<n*n;i++)        {            b[i] = ((double) rand()) / ((double) RAND_MAX) - 0.5;        }        /* Solve the equations A*X = B */        dgesv( &n, &n, a, &n, ipiv, b, &n, &info );        free(a);        free(b);        free(ipiv);        exit( 0 );} /* End of DGESV Example */

compiled on a Mac mini M1 with the command

Code Block clang -o dgesv_ex dgesv_ex.c -framework accelerate

uses only one core of the processor (as also shown by the activity monitor)

Code Block me@macmini-M1 ~ % time ./dgesv_ex ./dgesv_ex  35,54s user 0,27s system 100% cpu 35,758 total

I checked that the binary is of the right type:

Code Block me@macmini-M1 ~  % lipo -info dgesvNon-fat file: dgesv is architecture: arm64

As a comparaison, on my Intel MacBook Pro I get the following output :

Code Block me@macbook-intel ˜ % time ./dgesv_ex./dgesv_ex  142.69s user 0,51s system 718% cpu 19.925 total

Is it a known problem ? Maybe a compilation flag or else ?