QP (Quick Program Profiler) Release

QP: A Quick Program Profiler




QP is an exact and efficient program profiler. It rewrites a program's
executable file (a.out) by inserting code to record the execution
frequency of every basic block (straight-line sequence of instructions).
>From these counts, another program QP_STATS can calculate the execution
cost of procedures in the program. Unlike the Unix tools PROF and GPROF,
QP records exact execution frequency, not a statistical sample.


QP operates in two modes. In "slow" mode, it places a counter in each
basic block in a program--in the same manner as the MIPS tool PIXIE. In
"quick" mode, QP places counters on an infrequently-executed subset of the
edges in the program's control-flow graph. This placement can reduce the
cost of profiling by 3-4 times. Since there is no such thing as a free
lunch, quick profiling requires more program analysis and consequently
slows QP and QP_STATS. The additional cost to instrument a program and
report results, however, is small and is quickly gained back when
profiling long-running programs.


QP offers a number of advantages over existing systems:


    + On MIPS systems, QP typically requires less overhead than PIXIE
        and can profile programs that use signals. QP can also produces
        hierarchical profiles (like GPROF).


    + On SPARC-based systems, QP offers exact instruction counts,
        instead of a PC-histogram that is subject to quantization errors.
        QP also does not require recompilation of the program.


QP currently runs on MIPS and SPARC-based systems. I have verified the
ports on a DECstation and Sun 4 by profiling the entire SPEC benchmark
suite and other programs. A port to the the Motorola 88000 is under way.
QP is written to be portable--all of the machine-specific features are
collected in a single file. Porting to a new machine requires
approximately 1 month of effort.


The table below shows the overhead cost of slow and fast QP profiling and
the MIPS program PIXIE:


                        Slow Quick Pixie
SPEC Overhead Overhead Overhead
Benchmark % % %


gcc 224 78 169
espresso 185 98 113
spice 68 39 43
doduc 33 4 35
nasa7 8 6 3
li 136 85 157
eqntott 158 55 180
matrix30 13 13 7
fpppp 17 12 13
tomcatv 10 9 8


[Overhead measured on a DECstation 5000 with the SPEC benchmarks compiled
at -O2 to permit register scavengering. Overhead for QP is slightly
larger for SPEC benchmarks compiled at the standard level of -O3 or -O4.]


Documentation
=============


The algorithms in QP are described in a technical report:


        Thomas Ball and James R. Larus, "Optimally Profiling and Tracing
        Programs," Computer Sciences Technical Report #1031, University of
        Wisconsin, July 1991 (To appear POPL '92).


A postscript version of the technical report is available for anonymous
ftp from primost.cs.wisc.edu in the file ~ftp/pub/opt-prof-tracing.ps.Z




Obtaining QP
============


QP is distributed with the full source and a small amount of documentation.


QP is copyrighted by me and is distributed under license. A copy of the
license is available on primost.cs.wisc.edu in ~ftp/pub/qp-license.ps.Z or
it can be obtained by writing to me at the address below.


Send a signed copy of the license and a check for $300.00 (US) for a tape
copying charge. Please make the check payable to "Computer Sciences Fund
-- University of Wisconsin Foundation." The foundation's federal taxpayer
identification number is 39-074-3975.


James Larus
Computer Sciences Department
1210 West Dayton Street
University of Wisconsin
Madison, WI 53706


larus@cs.wisc.edu
(608) 262-9519
--

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