Restructuring Executables with fdpr

The fdpr (feedback-directed program restructuring) program optimizes executable modules for faster execution and more efficient use of real memory. It is available on AIX Version 4 systems as part of the Performance Toolbox for AIX. To determine whether fdpr is available on your system, use:

lslpp -lI perfagent.tools

If this package has been installed, fdpr is available.

fdpr processing takes place in three stages:

• The executable module to be optimized is instrumented to allow detailed performance-data collection.
• The instrumented executable is run in a workload provided by the user, and performance data from that run is recorded.
• The performance data is used to drive a performance-optimization process that results in a restructured executable module that should perform the workload that exercised the instrumented executable more efficiently. It is critically important that the workload used to drive fdpr closely match the actual use of the program. The performance of the restructured executable with workloads that differ substantially from that used to drive fdpr is unpredictable, but can be worse than that of the original executable.

As an example, the command:

fdpr -p ProgramName -R3 -x test.sh

would use the testcase test.sh to run an instrumented form of program ProgramName. The output of that run would be used to perform the most aggressive optimization (R3) of the program to form a new module called, by default, ProgramName.fdpr. The degree to which the optimized executable performed better in production than its unoptimized predecessor would depend largely on the degree to which test.sh successfully imitated the production workload.

Attention: The fdpr program incorporates advanced optimization algorithms that sometimes result in optimized executables that do not function in the same way as the original executable module. It is absolutely essential that any optimized executable be exhaustively tested before being used in any production situation; that is, before its output is trusted.

In summary, users of fdpr should:

• Take pains to use a workload to drive fdpr that is representative of the intended use.
• Exhaustively test the functioning of the resulting restructured executable.
• Use the restructured executable only on the workload for which it has been tuned.