mcexec: limit nr. of threads for non-OpenMP partitioned execution

executer/user/mcexec.c

@@ -2157,9 +2157,22 @@ int main(int argc, char **argv)
 		/* Leave some headroom for helper threads.. */
 		n_threads = atoi(getenv("OMP_NUM_THREADS")) + 4;
 	}
+	else {
+		/*
+		 * When running with partitioned execution, do not allow
+		 * more threads then the corresponding number of CPUs.
+		 */
+		if (nr_processes > 0) {
+			n_threads = (ncpu / nr_processes) + 4;
+
+			if (n_threads == 0) {
+				n_threads = 2;
+			}
+		}
 		else {
 			n_threads = ncpu;
 		}
+	}
 
 	/* 
 	 * XXX: keep thread_data ncpu sized despite that there are only