FULL PRODUCT VERSION :
java version "1.7.0"
Java(TM) SE Runtime Environment (build 1.7.0-b147)
Java HotSpot(TM) 64-Bit Server VM (build 21.0-b17, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
2.6.32-37-generic #81-Ubuntu SMP Fri Dec 2 20:32:42 UTC 2011 x86_64 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
I noticed a 20% reduction in performance of some benchmarks.  One shared property of the regressed benchmarks was that they both used ByteBuffers.

I then created some more targeted tests of ByteBuffers, simply putting and getting into them in a tight loop.  The test was essentially:

      byte[] data = 512*1024;
      final ByteBuffer buffer = ByteBuffer.wrap(data);

      while (buffer.position() < buffer.limit())
      {
         buffer.get();
      }

And for puts:

      final ByteBuffer buffer = ByteBuffer.wrap(data);

      while (buffer.position() < buffer.limit())
      {
         buffer.put((byte) 0);
      }

I then measured the average execution time for these to complete, in both Java 7, and a version of Java 6: java version "1.6.0_26"
Java(TM) SE Runtime Environment (build 1.6.0_26-b03)
Java HotSpot(TM) 64-Bit Server VM (build 20.1-b02, mixed mode)"

The difference in performance was striking:

Java 7 get() rate: 14.45 GiB / second
Java 6 get() rate: 21.78 GiB / second

Java 7 put() rate: 5.02 GiB / second
Java 6 put() rate: 9.69 GiB / second

REGRESSION.  Last worked in version 6u29

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Create a test as described in the description, execute it using Java 7, then execute it using Java 6.  Note the difference in runtime.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Performance on part or better in Java 7.
ACTUAL -
Performance was 2/3rds the speed for gets, and 1/2 for puts.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------

package org.cleversafe.benchmarks.processing;

import java.nio.ByteBuffer;

public class BugReproduce
{

   public static void main(final String args[])
   {
      final byte[] data = new byte[512 * 1024];

      long start = System.nanoTime();

      for (int i = 0; i < 10000; i++)
      {
         final ByteBuffer buffer = ByteBuffer.wrap(data);
         while (buffer.position() < buffer.limit())
         {
            buffer.get();
         }
      }

      long end = System.nanoTime();

      System.out.println("Execution took: " + (end - start) + " nanoseconds");

      start = System.nanoTime();

      for (int i = 0; i < 10000; i++)
      {
         final ByteBuffer buffer = ByteBuffer.wrap(data);
         while (buffer.position() < buffer.limit())
         {
            buffer.put((byte) 0);
         }
      }

      end = System.nanoTime();

      System.out.println("Execution took: " + (end - start) + " nanoseconds");
   }
}

---------- END SOURCE ----------