HP Fortran Programmer's Guide (B3908-90031; September 2011)

Performance and optimization
Using profilers
Chapter 6144
HP Caliper automatically runs to generate the flow-data information in a file named flow.data
in the current directory.
You can repeat this step multiple times with different program_arguments to create
aggregated profile information in the flow.data file to improve your program’s optimization.
If the flow.data file already exists in the current directory when you run your program, then
HP Caliper merges the results into the file. If you run your program multiple times in different
directories, then HP Caliper creates a separate flow.data file in each directory. You can
combine the files using the fdm(1) utility program, which is bundled with the HP C, HP aC++,
and Fortran 90 compilers.
When collecting PBO data, the more your program use scenarios resemble the ways in which
your program will actually be used, the more the compiler can optimize your program
specifically for how it is actually used.
When you make changes to your source files, you should delete the flow.data file before
collecting more PBO data on your program.
Step 3. Use the flow.data file as input to the compiler when you specify the +Oprofile=use option
on subsequent re-compiles.
/opt/ansic/bin/cc -Aa +O3 -o program +Oprofile=use program.c
The compiler uses the HP Caliper information to help optimize your program.
Note that the benefit of profile-based optimization is application dependent. Some programs may not
improve while others may improve significantly.
Comparing Program Performance
You can use HP Caliper’s other measurement features to explicitly see the results of using PBO.
An example process for comparing performance would be:
1. Compile your program with +Oprofile=collect to generate the executable to optimize.
2. Run your program to generate the profile data file. Use as many use scenarios as possible to collect
representative profile data.
3. Compile your program with +O3 to generate the baseline executable to compare against the fully
optimized executable.
4. Run HP Caliper on your +O3 executable with a configuration file such as total_cpu to measure
performance.
5. Recompile your program with +O3 optimization and +Oprofile=use to use the profile data collected
in Step 2 as input.