Ways to Improve Performance

Profile-Based Optimization

user's environment. Then, the optimizer will focus its efforts on the parts of the program that are critical to performance in the user's environment. You should not have to do a large number of profiling runs before the optimization phase. Usually it is adequate to select a small number of representative input data sets.

The flow.data File

When an instrumented program terminates with the exit(2) system call, special code in the 32-bit icrt0.o startup file or the 64-bit /usr/ccs/lib/pa20_64/fdp_init.ofile writes profile data to a file called flow.data in the current working directory. This file contains binary data, which cannot be viewed or updated with a text editor. The flow.data file is not updated when a process terminates without calling exit. That happens, for example, when a process aborts due to an unexpected signal, or when program calls exec(2) to replace itself with another program.

There are also certain non-terminating processes (such as servers, daemons, and operating systems) which never call exit. For these processes, you must programmatically write the profile data to the flow.data file. In order to do so, a process must call a routine called _write_counters(). This routine is defined in the icrt0.o file. A stub routine with the same name is present in the crt0.o file so that the source does not have to change when instrumentation is not being done.

If flow.data does not exist, the program creates it; if flow.data exists, the program updates the profile data.

As an example, suppose you have an instrumented program named prog.inst, and two representative input data files named input_file1 and input_file2. Then the following lines would create a flow.data file:

$ prog.inst < input_file1 $ ls flow.data

flow.data

$ prog.inst < input_file2

The flow.data file includes profile data from both input files.

To save the profile data to a file other than flow.data in the current working directory, use the FLOW_DATA environment variable as described in “Specifying a Different flow.data with FLOW_DATA”.

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HP 9000 specifications

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