Question

hi i am trying to get cpu load but i am getting per value more then 100% not understanding what wrong i am doing .. .

as i am using core i3 and having two Virtual machines on it and on one VM i am doing this task my source code is,

public class PerformanceMonitor {

    static long lastSystemTime      = 0;
        static long lastProcessCpuTime  = 0;
        public static int  availableProcessors = ManagementFactory.getOperatingSystemMXBean().getAvailableProcessors();
      // public static int  availableProcessors = Runtime.getRuntime().availableProcessors();
        public synchronized double getCpuUsage()
        {
            ManagementFactory.getThreadMXBean().setThreadCpuTimeEnabled(true);
            if ( lastSystemTime == 0 )
            {
                baselineCounters();
              //  return ;
            }

            long systemTime     = System.nanoTime();
            long processCpuTime = 0;

            processCpuTime = ManagementFactory.getThreadMXBean().getCurrentThreadCpuTime();
            double cpuUsage = (double) (processCpuTime - lastProcessCpuTime ) / ( systemTime - lastSystemTime )*100.0;

            lastSystemTime     = systemTime;
            lastProcessCpuTime = processCpuTime;

            return cpuUsage / availableProcessors;
        }

        private void baselineCounters()
        {
            lastSystemTime = System.nanoTime();

            lastProcessCpuTime = ManagementFactory.getThreadMXBean().getCurrentThreadCpuTime();
        }



        }

and i am using this class in my code ,

  public static void main(String[] args) {

             monitor = new PerformanceMonitor();
            for(int i=0 ; i<10000 ; i++){
                start();
                double usage = monitor.getCpuUsage();
                if(usage!=0)System.out.println("Current CPU usage in pourcentage : "+usage);
            }
        }

        private static void start() {
            int count=0;
            for(int i=0 ; i<100000 ; i++){
                count=(int) Math.random()*100;
            }
        }
}

i am getting output like this,

Current CPU usage in pourcentage : 114.32926829268293
Current CPU usage in pourcentage : 48.70208931963182
Current CPU usage in pourcentage : 193.08746862328633
Current CPU usage in pourcentage : 236.85457129322594

hopes for your suggestions thanks in advance

Answer 1

I suspect the interval is too short. The cpu counters on linux only update 100 times per second and you could be performing the loop in about 1/100th of a second meaning you get a very large error. Try increasing the length of the loop so it is a few seconds long.

---

I made the test longer and removed the / availableProcessors and I get numbers like this

Current CPU usage in percentage : 99.95763231535723
Current CPU usage in percentage : 99.94895863534565
Current CPU usage in percentage : 99.40642907762789
Current CPU usage in percentage : 99.96184668521532
Current CPU usage in percentage : 99.89017532820115
Current CPU usage in percentage : 99.91157680329947
Current CPU usage in percentage : 99.96919753553432
Current CPU usage in percentage : 99.94121334997978