Add an option to fix the message size

Test the question, is it the data volume, or the number of messages, that limits the wall clock time.

swiftmpistepsim.c

@@ -38,6 +38,10 @@ static int verbose = 0;
 /* Attempt to keep original injection time differences. */
 static int usetics = 1;
 
+/* Size of the messages we send. This overrides the logged values when not
+ * zero . */
+static size_t messagesize = 0;
+
 /* Set a data pattern and check we get this back, slow... */
 static int datacheck = 0;
 
@@ -383,6 +387,9 @@ static void pick_logs(void) {
     if (log->rank == myrank && log->activation) {
       if (log->type == task_type_send || log->type == task_type_recv) {
 
+        /* Override size if needed. */
+        if (messagesize > 0) log->size = messagesize;
+
         /* And keep this log. */
         log->data = NULL;
         reqs_queue[nr_reqs] = log;
@@ -411,7 +418,8 @@ static void pick_logs(void) {
 static void usage(char *argv[]) {
   fprintf(stderr, "Usage: %s [-vf] SWIFT_mpiuse-log-file.dat logfile.dat\n",
           argv[0]);
-  fprintf(stderr, " options: -v verbose, -f fast injections\n");
+  fprintf(stderr, " options: -v verbose, -f fast injections, "
+                  "-s message size (bytes)\n");
   fflush(stderr);
 }
 
@@ -437,7 +445,7 @@ int main(int argc, char *argv[]) {
   /* Handle the command-line, we expect a mpiuse data file to read and various
    * options. */
   int opt;
-  while ((opt = getopt(argc, argv, "vfd")) != -1) {
+  while ((opt = getopt(argc, argv, "vfds:")) != -1) {
     switch (opt) {
       case 'd':
         datacheck = 1;
@@ -448,6 +456,9 @@ int main(int argc, char *argv[]) {
       case 'v':
         verbose = 1;
         break;
+      case 's':
+        messagesize = atoll(optarg);
+        break;
       default:
         if (myrank == 0) usage(argv);
         return 1;
@@ -486,6 +497,10 @@ int main(int argc, char *argv[]) {
   if (myrank == 0) {
     message("Start of MPI tests");
     message("==================");
+    if (messagesize > 0) {
+      message(" ");
+      message("  Using fixed message size of %zd", messagesize);
+    }
     if (verbose) {
       if (!usetics) message("using fast untimed injections");
       if (datacheck)