code: public static String formatRate(long count, long time, TimeUnit units)
      {
          double rate = count * 1000.0;
          rate /= TimeUnit.MILLISECONDS.convert(time, units);
          return formatSize((long) rate) + "/s";
      }
docs: Given a size in bytes and a duration, format as a pretty
  throughput string.  The output will look like "15.4 MB/s".