Java Performance

The 3.1/3.1.1 releases provide a number of performance enhancements over version 3.0.1. For a set of medium-size applications (javac, for example) whose performance we measured, this release is 20% faster on average than the 3.0.1 release. Here are some of the reasons:

• MIPS n32 ABI: Use of the MIPS n32 ABI allows for more efficient parameter-passing and handling of the long and double data types in the code produced by the JIT compiler.
  
  
• Native Threads: Running with native threads on a multiprocessor machine can provide significant benefits for programs that are structured for multiple simultaneous threads of computation with little or no synchronization.
  
  
• Faster Synchronization: Thread synchronization (necessary for synchronized blocks and methods) has long been known to be a bottleneck in many Java virtual machines. In this release of our Java implementation, acquiring and releasing uncontested locks (the most common case) is much faster than with the 3.0.1 release. This has reduced the typical overhead of a synchronized method call by a factor of 3-4x.
  
  
• Per-method JIT: Previously, each class file was completely translated as it was loaded. Now, methods are translated the first time they are executed, so no unnecessary translation is done. The memory footprint of the JIT is now smaller (sometimes by 20-30%), and the capability to pre-translate class files using the javat command is no longer beneficial and has been removed, which saves disk space as well.

For some applications, we have actually seen slight degradation in performance since the 3.0.1 release. In most cases, we have isolated this degradation as being due to moving from Sun's JDK 1.1.3 release to 1.1.4 and then 1.1.5. If you have an important application for which performance has degraded since the 3.0.1 release, we would be interested in hearing from you.

For more information on the performance of Java on SGI systems, see our site on Silicon Surf.

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