float calculateCpuUsage(long systemTime, long cpuTime) {
    // 10000 = (Nano conversion factor / 100 for percentage)
    long denom = (systemTime - getLastSystemTime()) * 10000;
    return (float) (cpuTime - getLastProcessCpuTime()) / denom;
  }
@param systemTime Current system time.
@param cpuTime Last gathered cpu time.
@return The time (as a percentage) that this member's process time with respect to Statistics
        sample time interval. If process time between two sample time t1 & t2 is p1 and p2
        cpuUsage = ((p2-p1) * 100) / ((t2-t1).
geode-core/src/main/java/org/apache/geode/management/internal/beans/stats/VMStatsMonitor.java