Only one rank opens

benchmarks/Benchmark_usqcd.cc

@@ -842,10 +842,14 @@ public:
 
 int main (int argc, char ** argv)
 {
-
-  FP = fopen("Benchmark_usqcd.csv","w");
   Grid_init(&argc,&argv);
 
+  if (GlobalSharedMemory::WorldRank==0) { 
+    FP = fopen("Benchmark_usqcd.csv","w");
+  } else {
+    FP = fopen("/dev/null","w");
+  }
+
   CartesianCommunicator::SetCommunicatorPolicy(CartesianCommunicator::CommunicatorPolicySequential);
 #ifdef KNL
   LebesgueOrder::Block = std::vector<int>({8,2,2,2});