code: private void showAdminFormJobComparator(PrintWriter out, boolean advancedView) {
      out.print("<h2>Scheduling Mode</h2>\n");
      String curMode = scheduler.getJobComparator().toString();
      String advParam = advancedView ? "&advanced" : "";
      out.printf("<p>The scheduler is currently using <b>%s mode</b>.",
          generateSelect((Collection<String>)
              Arrays.asList("FAIR,DEFICIT,FIFO".split(",")),
              curMode, "/fairscheduler?setJobComparator=<CHOICE>" + advParam));
    }
docs: Print the administration form at the bottom of the page, which currently
  only includes the button for switching between FIFO and Fair Scheduling.