Merge pull request #3292 from martin-frbg/syrk_limit

Add lower limit for multithreading in xSYRK

benchmark/syrk.c

@@ -56,17 +56,20 @@ int main(int argc, char *argv[]){
 
   char uplo='U';
   char trans='N';
-
+  
   if ((p = getenv("OPENBLAS_UPLO"))) uplo=*p;
   if ((p = getenv("OPENBLAS_TRANS"))) trans=*p;
 
-  blasint m, i, j;
+  blasint m, i, j, l;
 
   int from =   1;
   int to   = 200;
   int step =   1;
+  int loops =  1;
+
+  if ((p = getenv("OPENBLAS_LOOPS"))) loops=*p;
 
-  double time1;
+  double time1,timeg;
 
   argc--;argv++;
 
@@ -95,9 +98,12 @@ int main(int argc, char *argv[]){
 
   for(m = from; m <= to; m += step)
   {
+    timeg = 0.;
 
     fprintf(stderr, " %6d : ", (int)m);
 
+    for(l = 0; l < loops; l++) {
+
     for(j = 0; j < m; j++){
       for(i = 0; i < m * COMPSIZE; i++){
 	a[(long)i + (long)j * (long)m * COMPSIZE] = ((FLOAT) rand() / (FLOAT) RAND_MAX) - 0.5;
@@ -111,8 +117,10 @@ int main(int argc, char *argv[]){
 
     end();
 
-    time1 = getsec();
-
+    timeg += getsec();
+    
+    } //loops
+    time1 = timeg / (double)loops;
     fprintf(stderr,
 	    " %10.2f MFlops\n",
 	    COMPSIZE * COMPSIZE * 1. * (double)m * (double)m * (double)m / time1 * 1.e-6);

interface/syrk.c

@@ -354,6 +354,17 @@ void CNAME(enum CBLAS_ORDER order, enum CBLAS_UPLO Uplo, enum CBLAS_TRANSPOSE Tr
 #endif
 
   args.common = NULL;
+#ifndef COMPLEX
+#ifdef DOUBLE
+  if (args.n < 100)
+#else
+  if (args.n < 200)
+#endif
+#else
+  if (args.n < 65)
+#endif
+  args.nthreads = 1;
+  else
   args.nthreads = num_cpu_avail(3);
 
   if (args.nthreads == 1) {