Hello Experts.

This program does not give expected performance boost on my P4 with
HyperThreading under Linux

/****************************************************************************/
public class ThreadTester implements Runnable {
   int id;

   public ThreadTester(int tid) {
       this.id = tid;
   }

   public void run() {
       System.out.println("Starting thread: " + id);

       long stime = System.currentTimeMillis();

       for (int i = 0; i < 20000; i++)
           for (int j = 0; j < 20000; j++) {
               double p = i * j;
               p = Math.sqrt(p);
           }

       stime = System.currentTimeMillis() - stime;

       System.out.println("Solution for thread " + id + " took " +
stime + " ms");
   }

   public static void main(String[] args) {

       if (args.length != 1) throw new
IllegalArgumentException("\n\nSyntax is 'java ThreadTester x' where x
is number of threads \n");

       int cpu = Integer.parseInt(args[0]);
       Thread[] t = new Thread[cpu];

       for (int i = 0; i < cpu; i++)
           t[i] = new Thread(new ThreadTester(i));

       for (int i = 0; i < cpu; i++)
           t[i].start();

       try {
           for (int i = 0; i < cpu; i++) {
               t[i].join();
           }
       } catch (InterruptedException e) {
           e.printStackTrace();
       }
   }
}
/**************************************************************************/

And this is my output

pc58410@gustav Impact $ java ThreadTester 1
Starting thread: 0
Solution for thread 0 took 5381 ms

pc58410@gustav Impact $ java ThreadTester 1
Starting thread: 0
Solution for thread 0 took 5379 ms

pc58410@gustav Impact $ java ThreadTester 2
Starting thread: 1
Starting thread: 0
Solution for thread 1 took 11247 ms
Solution for thread 0 took 11321 ms

pc58410@gustav Impact $ java ThreadTester 2
Starting thread: 1
Starting thread: 0
Solution for thread 1 took 11241 ms
Solution for thread 0 took 11325 ms

With an effective core distribution, this should have similar values as
the first runs (< 6000 ms)

What have I done wrong? I thought the JVM would make a good
distribution automatically?

Many thanks
/Jonas Forssell, Gothenburg, Sweden