Refs #153. Restore the original CPU affinity when calling openblas_set_num_threads(1).

Please read the issue on github.com for the detail.

driver/others/blas_server.c

@@ -770,6 +770,19 @@ void goto_set_num_threads(int num_threads) {
 
   if (num_threads < 1) num_threads = blas_num_threads;
 
+#ifndef NO_AFFINITY
+  if (num_threads == 1) {
+    if (blas_cpu_number == 1){
+      //OpenBLAS is already single thread.
+      return; 
+    }else{
+      //From multi-threads to single thread
+      //Restore the original affinity mask
+      gotoblas_set_affinity(-1);
+    }
+  }
+#endif
+
   if (num_threads > MAX_CPU_NUMBER) num_threads = MAX_CPU_NUMBER;
 
   if (num_threads > blas_num_threads) {
@@ -800,6 +813,13 @@ void goto_set_num_threads(int num_threads) {
     UNLOCK_COMMAND(&server_lock);
   }
 
+#ifndef NO_AFFINITY
+  if(blas_cpu_number == 1 && num_threads > 1){
+    //Restore the thread 0 affinity.
+    gotoblas_set_affinity(0);
+  }
+#endif
+
   blas_cpu_number  = num_threads;
 
 #if defined(ARCH_MIPS64)