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[unix-history] / usr / src / usr.bin / gprof / PSD.doc / intro.me

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.ls 2
.sh 1 "Programs to be Profiled"
.pp
Software research environments
normally include many large programs
both for  production use and for experimental investigation.
These programs are typically very modular,
in accordance with generally accepted principles
of good program design.
Often they consist of numerous small routines
that implement various abstractions.
Sometimes such large programs are written
by one programmer 
who has understood the requirements for
these abstractions, and has programmed them
appropriately.
More frequently the program has
had multiple authors and has
evolved over time, changing the demands placed
on the implementation of the abstractions without
changing the implementation itself.
Finally, the program may be assembled from a library
of abstraction implementations 
unexamined by the programmer.
.pp
Once a large program is executable,
it is often desirable to increase its speed,
especially if small portions of the program 
are found to dominate its execution time.
The purpose of the \fBgprof\fP profiling tool is to 
help the user evaluate alternative implementations
of abstractions.
In fact, we developed this tool in response to our efforts 
to improve a code generator we were writing [Graham82].
.pp
The \fBgprof\fP design takes advantage of the fact that the programs
to be measured are large, structured and hierarchical.
We provide a profile in which the execution time
for a set of routines that implement an
abstraction is collected and charged
to that abstraction.
The profile can be used to compare and assess the costs of
various implementations.
.pp
The profiler can be linked into a program without
special planning on the part of the programmer.
The overhead for using \fBgprof\fP is low;
both in terms of added execution time and the
volume of profiling information recorded.