HP C/aC++ for PA-RISC Software manual Instrumentation, Collecting Data for Profiling

When using profile-based optimization, please note the following:

•Numerical applications that perform the same calculations independent of the input data will only see a small performance boost.

•Profile-based optimization has the greatest impact on application performance when used with level 2 or greater optimizations.

•Profile-based optimization benefits most applications, especially large applications with multiple compilation units, such as compilers, editors, database managers, and user interface managers.

•Profile-based optimization should be enabled during the final stages of application development. To obtain the best performance, reprofile and reoptimize your application after making source code changes.

These steps are involved in performing profile-based optimization:

1.Instrumentation

2.Collecting Data for Profiling

3.Maintaining Profile Data Files

4.Performing Profile-Based Optimization

Instrumentation

To instrument your program, use the +Oprofile=collect option as follows:

aCC +Oprofile=collect -O -c sample.C

aCC +Oprofile=collect -O -o sample.exe sample.o

The first command line uses the +Oprofile=collect option to prepare the code for instrumentation. The -coption in the first command line suppresses linking and creates an object file called sample.o.

The second command line uses the -ooption to link sample.o into sample.exe. The +Oprofile=collect option instruments sample.exe with data collection code.

NOTE: Instrumented programs run slower than non-instrumented programs. Only use instrumented code to collect statistics for profile-based optimization.

Collecting Data for Profiling

To collect execution profile statistics, run your instrumented program with representative data as follows:

sample.exe < input.file1

sample.exe < input.file2

This step creates and logs the profile statistics to a file, by default called flow.data. The data collection file is a structured file that may be used to store the statistics from multiple test runs of different programs that you may have instrumented.

Maintaining Profile Data Files

Profile-based optimization stores execution profile data in a disk file. By default, this file is called flow.data and is located in your current working directory.

You can override the default name of the profile data file. This is useful when working on large programs or on projects with many different program files.

The FLOW_DATA environment variable can be used to specify the name of the profile data file with either the +Oprofile=collect or +Oprofile=use options.

The +Oprofile=use:filename command line option can be used to specify the name of the profile data file when used with the +Oprofile=use option.

Requesting Optimization 159