Add lower limit for multithreading

Author: martin-frbg

interface/zher.c

@@ -177,7 +177,10 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_UPLO Uplo, blasint n, FLOAT alpha,
   buffer = (FLOAT *)blas_memory_alloc(1);
 
 #ifdef SMP
-  nthreads = num_cpu_avail(2);
+  if (n < 100)
+    nthreads = 1;
+  else
+    nthreads = num_cpu_avail(2);
 
   if (nthreads == 1) {
 #endif