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  1. JDK
  2. JDK-6396953

Code runs slower after optimization when using server compiler

    Details

    • Type: Bug
    • Status: Closed
    • Priority: P4
    • Resolution: Duplicate
    • Affects Version/s: 6
    • Fix Version/s: 7
    • Component/s: hotspot
    • Labels:
    • Subcomponent:
    • CPU:
      x86
    • OS:
      linux

      Description

      FULL PRODUCT VERSION :
      java version "1.6.0-beta2"
      Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-beta2-b72)
      Java HotSpot(TM) Client VM (build 1.6.0-beta2-b72, mixed mode, sharing)

      ADDITIONAL OS VERSION INFORMATION :
      Linux localhost.localdomain 2.6.11-1.1369_FC4 #1 Thu Jun 2 22:55:56 EDT 2005 i686 athlon i386 GNU/Linux

      EXTRA RELEVANT SYSTEM CONFIGURATION :
      Tested on:
      AMD Duron 800
      Amd Athlon X2 4400+

      A DESCRIPTION OF THE PROBLEM :
      When executing the sample code the code runs first quite fast till hotspot server completly has "optimized" all methods when suddenly performance falls down and stays there.

      There are 3 tests, test 1 and 2 are slower after optimization, only test 3 runs faster after optimization using the server runtime (C2).
      I marked this one as regression since the strange behaviour was introduced with java-1.4, java-1.3.1 worked quite well.
      With the client jvm a small speedup can be measured during execution, how it should be.

      Here are my benchmark results with the code above on a Duron800, a quite outdated CPU:
      1.6.0-beta2-b72 / Java HotSpot(TM) Server VM
      2.871 secs 2.827 secs 5.525 secs
      2.742 secs 2.772 secs 5.473 secs
      4.665 secs 4.336 secs 2.784 secs <<--- What happens here?
      4.661 secs 4.334 secs 2.78 secs

      1.4.2_06-b03 / Java HotSpot(TM) Server VM
      3.104 secs 3.01 secs 4.953 secs
      4.827 secs 4.2 secs 2.82 secs <<-- Here the same, but earlier
      4.832 secs 4.207 secs 2.823 secs
      4.832 secs 4.208 secs 2.829 secs

      1.3.1_16-b06 / Java HotSpot(TM) Server VM
      6.312 secs 6.292 secs 5.875 secs
      4.729 secs 4.663 secs 4.676 secs -->> No bug, but slow. right behaviour, everything gets faster...
      4.72 secs 4.686 secs 4.666 secs


      This is the output of PrintCompilation, tests are labeld with (test):
      1.6.0-beta2-b72 / Java HotSpot(TM) Server VM
      1% ArrayDemo::test1 @ 46 (103 bytes)
      3.077 secs(1) 2% ArrayDemo::test2 @ 46 (100 bytes)
      3.033 secs(2) 3% ArrayDemo::test3 @ 46 (87 bytes)
      5.65 secs(3)
      1 ArrayDemo::test1 (103 bytes)
      2.946 secs(1) 2 ArrayDemo::test2 (100 bytes)
      2.975 secs(2) 3 ArrayDemo::test3 (87 bytes)
      5.599 secs(3)
      4.778 secs 4.425 secs 2.982 secs

      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      run the sample code using the java server runtime.

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      when hotspot has finished with compilation performance should be better instead of worse.
      ACTUAL -
      when hotspot has finished compilation the test1 and test2 run slower than before.

      REPRODUCIBILITY :
      This bug can be reproduced always.

      ---------- BEGIN SOURCE ----------
      public class ArrayDemo
      {
      private final int[] a = new int[20*1024];
      private final int[] b = new int[a.length];
      private final int LOOPS = 5000;

      public ArrayDemo()
      {
      init = false;

      for(int k = 0; k < 500; k++) {
      test1(LOOPS);
      test2(LOOPS);
      test3(LOOPS);
      System.out.println();
      }
      }

      private long start;
      private boolean init = true;

      private void end()
      {
      if(init) return;
      long dur = (System.currentTimeMillis() - start);
      System.out.print((dur/1000d)+" secs ");
      }

      private void test1(final int loops)
      {
      start = System.currentTimeMillis();

      for(int k = 0; k < loops; k++) {
      int ia = 0;
      int ib = 0;
      while(true) {
      int t = a.length - ia;
      if(t == 0) break;
      if(t > 1024) t = 1024;
      do {
      if(b[ib] == 0xfe)break;
      a[ia++] = b[ib++];
      } while(--t > 0);
      }
      }

      end();
      }

      private void test2(final int loops)
      {
      start = System.currentTimeMillis();

      for(int k = 0; k < loops; k++) {
      int ia = 0;
      int ib = 0;
      while(true) {
      int t = a.length - ia;
      if(t == 0) break;
      if(t > 1024) t = 1024;
      do {
      if(b[ib] == 0xfe)/*break*/;
      a[ia++] = b[ib++];
      } while(--t > 0);
      }
      }

      end();
      }

      private void test3(final int loops)
      {
      start = System.currentTimeMillis();

      for(int k = 0; k < loops; k++) {
      int ia = 0;
      int ib = 0;
      while(true) {
      int t = a.length - ia;
      if(t == 0) break;
      if(t > 1024) t = 1024;
      do {
      /* if(b[ib] == 0xfe)break;*/
      a[ia++] = b[ib++];
      } while(--t > 0);
      }
      }

      end();
      }

      public static void main(String[] args)
      {
      System.out.println(System.getProperty("java.vm.version")+" / "+System.getProperty("java.vm.name"));
      new ArrayDemo();
      }
      }
      ---------- END SOURCE ----------

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              • Assignee:
                cfang Changpeng Fang (Inactive)
                Reporter:
                rmandalasunw Ranjith Mandala (Inactive)
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                • Created:
                  Updated:
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