OPTIMIZING THE JAVA VIRTUAL MACHINE INSTRUCTION SET BY ...

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B.5.2
Multicode Timing Script
The multicode timing script performs tasks similar to those conducted by the despecialization
timing scripts. However, it must also generate a new version of the Kaffe
virtual machine which supports multicodes. The timing scripts used for the despecialization
studies did not perform this task because they used each virtual machine
in its original, unmodified form.
The timing script was capable of measuring the performance of several benchmarks
and rule files in a single run. An appropriate virtual machine was built for each rule
file tested. The output generated from the script included an indication of each rule
file tested and the actual output generated when the benchmarks were executed. By
default, the script executed each benchmark six times although this behaviour could
be overridden using a command line parameter.
The output generated by the timing script was processed by a second script. It
was responsible for reporting the average performance for each condition tested after
discarding the highest and lowest values achieved in order to minimize the impact of
outliers. All of the performance results generated by this second script were reported
as a percentage of the execution time achieved by the first test condition tested. As a
result, the first test condition run was normally the original, unmodified benchmark.
B.6 Putting the Pieces Together
Figure B.1 shows the process followed in order to generate the despecialization results
presented in Chapter 5. The left column illustrates the steps that were taken using
the scripts described in the previous sections in order determine what order the despecializations
should be performed in. The steps in the right column show the steps
taken to gather the performance results. The initial despecialization study presented
in Chapter 4 did not perform any profiling. Consequently, it only performed the steps
shown on the right side of the diagram.
The process followed to gather multicode performance results is shown in Figure
B.2. This process was followed for the studies presented in both Chapter 7 and
Chapter 8. The left side of the diagram shows the process followed in order to
determine which bytecode sequences should be replaced by multicodes. Once this
determination was made, the steps on the right side of the diagram were followed in
order to determine the impact the multicodes had on application performance.