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This is gprof.info, produced by makeinfo version 4.8 from
/home/xpgcust/tree/RI-2019.1/ib/p4root/Xtensa/Software/binutils/gprof/gprof.texi.
10/2018
Copyright (C) 1988, 1992, 1997, 1998, 1999, 2000, 2001, 2003, 2007,
2008, 2009 Free Software Foundation, Inc.
Copyright (C) 1999-2009 Tensilica, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled "GNU
Free Documentation License".
This publication is provided "AS IS." Tensilica, Inc. (hereafter
"Tensilica") does not make any warranty of any kind, either expressed
or implied, including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose. Information in
this document is provided solely to enable system and software
developers to use Tensilica(R) processors. Unless specifically set
forth herein, there are no express or implied patent, copyright or any
other intellectual property rights or licenses granted hereunder to
design or fabricate Tensilica integrated circuits or integrated
circuits based on the information in this document. Tensilica does not
warrant that the contents of this publication, whether individually or
as one or more groups, meets your requirements or that the publication
is error-free. This publication could include technical inaccuracies
or typographical errors. Changes may be made to the information
herein, and these changes may be incorporated in new editions of this
publication.
The following terms are trademarks or registered trademarks of
Tensilica, Inc.: FLIX, OSKit, Sea of Processors, Tensilica, Vectra,
Xplorer, XPRES, and Xtensa. All other trademarks and registered
trademarks are the property of their respective companies.

File: gprof.info, Node: Top, Next: Revisions, Up: (dir)
GNU Profiler User's Guide
*************************
This manual describes the GNU profiler, `gprof', and how you can use it
to determine which parts of a program are taking most of the execution
time. We assume that you know how to write, compile, and execute
programs. GNU `gprof' was written by Jay Fenlason.
This document is distributed under the terms of the GNU Free
Documentation License version 1.3. A copy of the license is included
in the section entitled "GNU Free Documentation License".
* Menu:
* Revisions:: Changes from previous versions.
* Introduction:: What profiling means, and why it is useful.
* Compiling:: How to compile your program for profiling.
* Executing:: Executing your program to generate profile data
* Invoking:: How to run `gprof', and its options
* Output:: Interpreting `gprof''s output
* Inaccuracy:: Potential problems you should be aware of
* GNU Free Documentation License:: GNU Free Documentation License
* History:: History of this document

File: gprof.info, Node: Revisions, Next: Introduction, Prev: Top, Up: Top
Changes from Previous Versions
******************************
The following changes were made for version 14 of the Xtensa Tools:
* Upgraded from version 2.18 to version 2.20 of the GNU Binary
Utilities.

File: gprof.info, Node: Introduction, Next: Compiling, Prev: Revisions, Up: Top
1 Introduction to Profiling
***************************
Profiling allows you to learn where your program spent its time and
which functions called which other functions while it was executing.
This information can show you which pieces of your program are slower
than you expected, and might be candidates for rewriting to make your
program execute faster. It can also tell you which functions are being
called more or less often than you expected. This may help you spot
bugs that had otherwise been unnoticed.
Since the profiler uses information collected during the actual
execution of your program, it can be used on programs that are too
large or too complex to analyze by reading the source. However, how
your program is run will affect the information that shows up in the
profile data. If you don't use some feature of your program while it
is being profiled, no profile information will be generated for that
feature.
Tensilica supports two options for collecting profile information.
First, the Xtensa instruction set simulator (ISS) can directly generate
the profile data. This is the easiest, most accurate, and most
flexible option. If the profile data for your program needs to reflect
interactions with real hardware, or if the ISS profiling is too slow,
the second option is to profile your program running on a hardware
implementation of your system. Hardware profiling requires certain
Xtensa processor features, and it uses statistical sampling, which
makes the results less accurate. Other profiling tools may be
available from third-party operating system vendors.
Profiling with the Xtensa ISS has several advantages over hardware
profiling:
* You do not need to compile the Xtensa program with special options
(e.g., `-hwpg') before profiling it.
* There is no instrumentation code added to the Xtensa program, so
the profile results are not distorted by any extra code.
* The Xtensa ISS can easily record the execution of every
instruction, so there is no need to rely on statistical
approximations like PC-sampling.
* Instead of counting execution cycles, the Xtensa ISS can optionally
record profile data for other events, such as cache misses. You
can then use `xt-gprof' or Xplorer to view a profile of these
other events.
Hardware profiling also imposes certain requirements on your Xtensa
system. The processor must include the Xtensa Debug Option, so that it
can send the profile data back to a host system via the On-Chip
Debugging (OCD) interface connected to the GNU Debugger (GDB). A
dedicated Xtensa timer, preferably with a dedicated interrupt level, is
required to control the PC sampling. For more information, please see
the description of hardware profiling in the `Xtensa Software
Development Toolkit User's Guide'.
Regardless of whether you use the ISS or hardware profiling,
Tensilica's `xt-gprof' uses a custom file format for the profile data.
This allows profiling of discontiguous text regions and avoids
inaccuracies related to combining the execution counts for adjacent
instructions.
Profiling has several steps:
* You must compile and link your program. Depending on whether you
are using the Xtensa ISS or hardware profiling, and depending on
what `gprof' options you want to use, you may need to specify
certain options to the compiler. *Note Compiling a Program for
Profiling: Compiling.
* You must execute your program to generate a profile data file.
*Note Executing the Program: Executing.
* You must run `xt-gprof' to analyze the profile data. *Note
`gprof' Command Summary: Invoking.
The next three chapters explain these steps in greater detail.
The profile data files may contain several kinds of data. One
section is a histogram of the events (cycle count, cache misses, etc.)
for each Xtensa instruction. Another section records the execution
count for each call-graph edge. The histogram counts and call-graph
edge counts are read and analyzed by `gprof'.
Several forms of output are available from the analysis.
The "flat profile" shows the total histogram counts for each
function, and how many times that function was called. If you simply
want to know which functions have the highest counts (i.e., which
functions burn most of the cycles, have the most cache misses, etc.),
it is stated concisely here. *Note The Flat Profile: Flat Profile.
The "call graph" shows, for each function, which functions called
it, which other functions it called, and how many times. There is also
an estimate of the histogram counts for the subroutines of each
function. This can suggest places where you might try to eliminate
function calls that use a lot of time. *Note The Call Graph: Call
Graph.
The "annotated source" listing is a copy of the program's source
code, labeled with the number of times each line of the program was
executed. *Note The Annotated Source Listing: Annotated Source.

File: gprof.info, Node: Compiling, Next: Executing, Prev: Introduction, Up: Top
2 Compiling a Program for Profiling
***********************************
For profiling with the Xtensa ISS, nothing special is required when
compiling your program. The profile data is collected by the ISS, so
no instrumentation code needs to be added to your program. You may
want to compile with `-g' to collect debugging information, which is
used for line-by-line profiling. *Note Line-by-line Profiling:
Line-by-line.
For Tensilica's hardware profiling, the first step in generating
profile information for your program is to compile and link it with
profiling enabled.
To compile a source file for profiling, specify the `-hwpg=N' option
when you run the compiler, where N is the timer number used for
profiling. (This is in addition to the options you normally use.)
To link the program for profiling, use the XCC compiler to do the
linking and simply specify `-hwpg=N' in addition to your usual options.
The same option, `-hwpg', alters either compilation or linking to do
what is necessary for profiling. Here are examples:
xt-xcc -g -c myprog.c utils.c -hwpg=1
xt-xcc -o myprog myprog.o utils.o -hwpg=1
The `-hwpg' option also works with a command that both compiles and
links:
xt-xcc -o myprog myprog.c utils.c -g -hwpg=1
Note: If the `-hwpg' option is not part of your compilation options,
but only your link options, you will avoid adding instrumentation code
to your program, but no call-graph data will be gathered and when you
run `gprof' you will get an error message like this:
xt-gprof: gmon.out file is missing call-graph data
If you add the `-Q' switch to suppress the printing of the call
graph data you will still be able to see the time samples:
Flat profile:
self total
cumulative self cycles cycles
% cycles cycles calls /call /call name
(K) (K) (K) (K)
44.12 7.69 7.69 zazLoop
35.29 13.84 6.15 main
20.59 17.42 3.59 bazMillion
If you compile only some of the modules of the program with `-hwpg',
you can still profile the program, but you won't get complete
information about the modules that were compiled without `-hwpg'. The
only information you get for the functions in those modules is the
total time spent in them; there is no record of how many times they
were called, or from where. This will not affect the flat profile
(except that the `calls' field for the functions will be blank), but
will greatly reduce the usefulness of the call graph.
If you wish to perform line-by-line profiling, you will also need to
specify the `-g' option, instructing the compiler to insert debugging
symbols into the program that match program addresses to source code
lines. *Note Line-by-line Profiling: Line-by-line.

File: gprof.info, Node: Executing, Next: Invoking, Prev: Compiling, Up: Top
3 Executing the Program
***********************
Once the program is compiled, you must run it in order to generate the
information that `gprof' needs. The way you run the program--the
arguments and input that you give it--may have a dramatic effect on
what the profile information shows. The profile data will describe the
parts of the program that were activated for the particular input you
use. For example, if the first command you give to your program is to
quit, the profile data will show the time used in initialization and in
cleanup, but not much else.
* Menu:
* Xtensa ISS:: Profiling with the Xtensa ISS
* Xtensa Hardware:: Collecting profile data from Xtensa hardware

File: gprof.info, Node: Xtensa ISS, Next: Xtensa Hardware, Up: Executing
3.1 Profiling with the Xtensa ISS
=================================
If you are profiling with the Xtensa instruction set simulator (ISS),
you can specify two kinds of options to the ISS profiling client:
* What events to profile: The default is to count the cycles spent
executing each instruction, but you can also profile other events
such as cache misses or pipeline interlocks.
* The output file name: This is the raw data file to be read by
`gprof'. If more than one kind of event is being profiled at the
same time, the name you specify is used as the base name and the
ISS appends a different suffix for each output file.
For example, to profile instruction cache misses and write the
results to a file named `misses.out', the ISS would be invoked with the
`--client_cmds="profile --icmiss misses.out"' option. Please see the
description of the `profile' client in the `Xtensa Instruction Set
Simulator (ISS) User's Guide' for more information about these options.
If you only want to profile cycle counts, you can simply invoke the
ISS with the `--profile=OUTFILE' option. This is equivalent to
`--client_cmds="profile OUTFILE"'. By default, `gprof' will expect the
profile information to be in a file called `gmon.out'. Therefore, it
is simplest to just use `--profile=gmon.out'.
If your program runs for a long time and you want to use the fast
functional simulation mode of the ISS (the `--turbo' option), you can
still collect profile data. Nothing special is required to profile
instruction counts (with `--client_cmds="profile --instructions"') in
this mode. Other kinds of profile data require statistical sampling,
using the `--sample' ISS option to periodically switch to the
cycle-accurate simulation mode. You can specify the `--sample_insns'
and `--sample_ratio' ISS options to control the size and frequency of
the cycle-accurate samples. The sampled results are automatically
extrapolated by the ISS to the fast functional portions of the
simulation. See the `Xtensa Instruction Set Simulator (ISS) User's
Guide' for more information.
Depending on the kinds of events you want to profile, you may need to
specify other ISS options. By default, the Xtensa ISS does not
simulate the memory system; all memory references are assumed to be in
cache. Use the `--mem_model' option if you want the cycle counts to
reflect the effects of caches and local memory. If you are profiling
cache misses, you will also need to use the `--mem_model' option.

File: gprof.info, Node: Xtensa Hardware, Prev: Xtensa ISS, Up: Executing
3.2 Xtensa Hardware Profiling
=============================
After compiling your program for hardware profiling, run it on the
hardware as you would normally debug it, using either `xt-gdb' or
`xplorer --debug'. When your program calls `exit', the debugger will
write the profile data to a file with a name composed of `gmon.out'
followed by a unique suffix. If your program does not call `exit', you
can interrupt it and use the debugger to call the
`xt_profile_save_and_reset' function, which will write out the profile
data. You can exit from the debugger after the profile data has been
written out. See the `Xtensa Software Development Toolkit User's
Guide' for details on using hardware profiling.

File: gprof.info, Node: Invoking, Next: Output, Prev: Executing, Up: Top
4 `gprof' Command Summary
*************************
After you have a profile data file `gmon.out', you can run `gprof' to
interpret the information in it. The `gprof' program prints a flat
profile and a call graph on standard output. Typically you would
redirect the output of `gprof' into a file with `>'.
You run `gprof' like this:
xt-gprof OPTIONS [EXECUTABLE-FILE [PROFILE-DATA-FILES...]] [> OUTFILE]
Here square-brackets indicate optional arguments.
If you omit the executable file name, the file `a.out' is used. If
you give no profile data file name, the file `gmon.out' is used. If
any file is not in the proper format, or if the profile data file does
not appear to belong to the executable file, an error message is
printed.
You can give more than one profile data file by entering all their
names after the executable file name; then the statistics in all the
data files are summed together.
The order of these options does not matter.
* Menu:
* Output Options:: Controlling `gprof''s output style
* Analysis Options:: Controlling how `gprof' analyzes its data
* Miscellaneous Options::
* Symspecs:: Specifying functions to include or exclude

File: gprof.info, Node: Output Options, Next: Analysis Options, Up: Invoking
4.1 Output Options
==================
These options specify which of several output formats `gprof' should
produce.
Many of these options take an optional "symspec" to specify
functions to be included or excluded. These options can be specified
multiple times, with different symspecs, to include or exclude sets of
symbols. *Note Symspecs: Symspecs.
Specifying any of these options overrides the default (`-p -q'),
which prints a flat profile and call graph analysis for all functions.
`-A[SYMSPEC]'
`--annotated-source[=SYMSPEC]'
The `-A' option causes `gprof' to print annotated source code. If
SYMSPEC is specified, print output only for matching symbols.
*Note The Annotated Source Listing: Annotated Source.
`-b'
`--brief'
If the `-b' option is given, `gprof' doesn't print the verbose
blurbs that try to explain the meaning of all of the fields in the
tables. This is useful if you intend to print out the output, or
are tired of seeing the blurbs.
`-C[SYMSPEC]'
`--exec-counts[=SYMSPEC]'
The `-C' option causes `gprof' to print a tally of functions and
the number of times each was called. If SYMSPEC is specified,
print tally only for matching symbols.
If you profile instruction counts (not cycles) with the Xtensa
ISS, that is, if you run ISS with `--client_cmds="profile
--instructions"', invoking `gprof' with the `-l' option, along
with `-C', will cause basic-block execution counts to be tallied
and displayed.
`-i'
`--file-info'
The `-i' option causes `gprof' to display summary information
about the profile data file(s) and then exit. The number of
histogram, call graph, and basic-block count records is displayed.
`-I DIRS'
`--directory-path=DIRS'
The `-I' option specifies a list of search directories in which to
find source files. Environment variable GPROF_PATH can also be
used to convey this information. Used mostly for annotated source
output.
`-J[SYMSPEC]'
`--no-annotated-source[=SYMSPEC]'
The `-J' option causes `gprof' not to print annotated source code.
If SYMSPEC is specified, `gprof' prints annotated source, but
excludes matching symbols.
`-L'
`--print-path'
Normally, source filenames are printed with the path component
suppressed. The `-L' option causes `gprof' to print the full
pathname of source filenames, which is determined from symbolic
debugging information in the image file and is relative to the
directory in which the compiler was invoked.
`-p[SYMSPEC]'
`--flat-profile[=SYMSPEC]'
The `-p' option causes `gprof' to print a flat profile. If
SYMSPEC is specified, print flat profile only for matching symbols.
*Note The Flat Profile: Flat Profile.
`-P[SYMSPEC]'
`--no-flat-profile[=SYMSPEC]'
The `-P' option causes `gprof' to suppress printing a flat profile.
If SYMSPEC is specified, `gprof' prints a flat profile, but
excludes matching symbols.
`-q[SYMSPEC]'
`--graph[=SYMSPEC]'
The `-q' option causes `gprof' to print the call graph analysis.
If SYMSPEC is specified, print call graph only for matching symbols
and their children. *Note The Call Graph: Call Graph.
`-Q[SYMSPEC]'
`--no-graph[=SYMSPEC]'
The `-Q' option causes `gprof' to suppress printing the call graph.
If SYMSPEC is specified, `gprof' prints a call graph, but excludes
matching symbols.
`-t'
`--table-length=NUM'
The `-t' option causes the NUM most active source lines in each
source file to be listed when source annotation is enabled. The
default is 10.
`-y'
`--separate-files'
This option affects annotated source output only. Normally,
`gprof' prints annotated source files to standard-output. If this
option is specified, annotated source for a file named
`path/FILENAME' is generated in the file `FILENAME-ann'. If the
underlying file system would truncate `FILENAME-ann' so that it
overwrites the original `FILENAME', `gprof' generates annotated
source in the file `FILENAME.ann' instead (if the original file
name has an extension, that extension is _replaced_ with `.ann').
`-Z[SYMSPEC]'
`--no-exec-counts[=SYMSPEC]'
The `-Z' option causes `gprof' not to print a tally of functions
and the number of times each was called. If SYMSPEC is specified,
print tally, but exclude matching symbols.
`-r'
`--function-ordering'
The `--function-ordering' option causes `gprof' to print a
suggested function ordering for the program based on profiling
data. This option suggests an ordering which may improve paging,
tlb and cache behavior for the program on systems which support
arbitrary ordering of functions in an executable.
The exact details of how to force the linker to place functions in
a particular order is system dependent and out of the scope of this
manual.
`-R MAP_FILE'
`--file-ordering MAP_FILE'
The `--file-ordering' option causes `gprof' to print a suggested
.o link line ordering for the program based on profiling data.
This option suggests an ordering which may improve paging, tlb and
cache behavior for the program on systems which do not support
arbitrary ordering of functions in an executable.
Use of the `-a' argument is highly recommended with this option.
The MAP_FILE argument is a pathname to a file which provides
function name to object file mappings. The format of the file is
similar to the output of the program `nm'.
c-parse.o:00000000 T yyparse
c-parse.o:00000004 C yyerrflag
c-lang.o:00000000 T maybe_objc_method_name
c-lang.o:00000000 T print_lang_statistics
c-lang.o:00000000 T recognize_objc_keyword
c-decl.o:00000000 T print_lang_identifier
c-decl.o:00000000 T print_lang_type
...
To create a MAP_FILE with GNU `nm', type a command like `nm
--extern-only --defined-only -v --print-file-name program-name'.
`-T'
`--traditional'
The `-T' option causes `gprof' to print its output in
"traditional" BSD style.
`-w WIDTH'
`--width=WIDTH'
Sets width of output lines to WIDTH. Currently only used when
printing the function index at the bottom of the call graph.
`-x'
`--all-lines'
This option affects annotated source output only. By default,
only the lines at the beginning of a basic-block are annotated.
If this option is specified, every line in a basic-block is
annotated by repeating the annotation for the first line. This
behavior is similar to `tcov''s `-a'.
`--demangle[=STYLE]'
`--no-demangle'
These options control whether C++ symbol names should be demangled
when printing output. The default is to demangle symbols. The
`--no-demangle' option may be used to turn off demangling.
Different compilers have different mangling styles. The optional
demangling style argument can be used to choose an appropriate
demangling style for your compiler.

File: gprof.info, Node: Analysis Options, Next: Miscellaneous Options, Prev: Output Options, Up: Invoking
4.2 Analysis Options
====================
`-a'
`--no-static'
The `-a' option causes `gprof' to suppress the printing of
statically declared (private) functions. (These are functions
whose names are not listed as global, and which are not visible
outside the file/function/block where they were defined.) Time
spent in these functions, calls to/from them, etc., will all be
attributed to the function that was loaded directly before it in
the executable file. This option affects both the flat profile
and the call graph.
`-c'
`--static-call-graph'
The `-c' option causes the call graph of the program to be
augmented by a heuristic which examines the text space of the
object file and identifies function calls in the binary machine
code. Since normal call graph records are only generated when
functions are entered, this option identifies children that could
have been called, but never were. Calls to functions that were
not compiled with profiling enabled are also identified, but only
if symbol table entries are present for them. Calls to dynamic
library routines are typically _not_ found by this option.
Parents or children identified via this heuristic are indicated in
the call graph with call counts of `0'.
`-D'
`--ignore-non-functions'
The `-D' option causes `gprof' to ignore symbols which are not
known to be functions. This option will give more accurate
profile data on systems where it is supported (Solaris and HPUX for
example).
`-f'
`--function-line'
The `-f' option enables line-by-line profiling where all the lines
for a function are grouped together in the flat profile.
Specifically, the flat profile entries are first sorted by
function in decreasing order of the histogram counts for the
function as a whole, and then sorted by line within each function,
again in decreasing order of histogram counts. Aside from the
order of the flat profile entries, this option is the same as the
`-l' option. The program must be compiled with a `-g' option so
that line number information is available.
`-k FROM/TO'
The `-k' option allows you to delete from the call graph any arcs
from symbols matching symspec FROM to those matching symspec TO.
`-K LOWPC:HIGHPC'
`--pc-range LOWPC:HIGHPC'
The `-K' option allows you to exclude profile data outside a
specific range of code. Histogram hits and call graph arcs with
addresses lower than LOWPC or higher than HIGHPC are simply
ignored. The addresses may be specified as decimal, hexadecimal or
octal values, with a `0' prefix for octal values or a `0x' prefix
for hexadecimal values. This option may be useful when analyzing
the performance of a region of code that would otherwise be
obscured by the rest of the program.
`-l'
`--line'
The `-l' option enables line-by-line profiling, which causes
histogram counts to be charged to individual source code lines,
instead of functions.
If you profile instruction counts (not cycles) with the Xtensa
ISS, that is, if you run ISS with `--client_cmds="profile
--instructions"', this option will also identify how many times
each line of code was executed. The program must be compiled with
a `-g' option so that line number information is available. While
line-by-line profiling can help isolate where in a large function
a program is spending its time, it also significantly increases
the running time of `gprof', and magnifies statistical
inaccuracies for hardware profiling. *Note Statistical Sampling
Error: Sampling Error.
`-m NUM'
`--min-count=NUM'
This option affects execution count output only. Symbols that are
executed less than NUM times are suppressed.
`-nSYMSPEC'
`--time=SYMSPEC'
The `-n' option causes `gprof', in its call graph analysis, to
only propagate times for symbols matching SYMSPEC.
`-NSYMSPEC'
`--no-time=SYMSPEC'
The `-n' option causes `gprof', in its call graph analysis, not to
propagate times for symbols matching SYMSPEC.
`-SFILENAME'
`--external-symbol-table=FILENAME'
The `-S' option causes `gprof' to read an external symbol table
file, such as `/proc/kallsyms', rather than read the symbol table
from the given object file (the default is `a.out'). This is useful
for profiling kernel modules.
`-z'
`--display-unused-functions'
If you give the `-z' option, `gprof' will mention all functions in
the flat profile, even those that were never called, and that had
no time spent in them. This is useful in conjunction with the
`-c' option for discovering which routines were never called.

File: gprof.info, Node: Miscellaneous Options, Next: Symspecs, Prev: Analysis Options, Up: Invoking
4.3 Miscellaneous Options
=========================
`-d[NUM]'
`--debug[=NUM]'
The `-d NUM' option specifies debugging options. If NUM is not
specified, enable all debugging.
`-h'
`--help'
The `-h' option prints command line usage.
`-ONAME'
`--file-format=NAME'
Selects the format of the profile data files. Recognized formats
are `auto' (the default), `bsd', `4.4bsd', `magic', and `prof'
(not yet supported).
`-s'
`--sum'
The `-s' option causes `gprof' to summarize the information in the
profile data files it read in, and write out a profile data file
called `gmon.sum', which contains all the information from the
profile data files that `gprof' read in. The file `gmon.sum' may
be one of the specified input files; the effect of this is to
merge the data in the other input files into `gmon.sum'.
Eventually you can run `gprof' again without `-s' to analyze the
cumulative data in the file `gmon.sum'.
`-v'
`--version'
The `-v' flag causes `gprof' to print the current version number,
and then exit.

File: gprof.info, Node: Symspecs, Prev: Miscellaneous Options, Up: Invoking
4.4 Symspecs
============
Many of the output options allow functions to be included or excluded
using "symspecs" (symbol specifications), which observe the following
syntax:
filename_containing_a_dot
| funcname_not_containing_a_dot
| linenumber
| ( [ any_filename ] `:' ( any_funcname | linenumber ) )
Here are some sample symspecs:
`main.c'
Selects everything in file `main.c'--the dot in the string tells
`gprof' to interpret the string as a filename, rather than as a
function name. To select a file whose name does not contain a
dot, a trailing colon should be specified. For example, `odd:' is
interpreted as the file named `odd'.
`main'
Selects all functions named `main'.
Note that there may be multiple instances of the same function name
because some of the definitions may be local (i.e., static).
Unless a function name is unique in a program, you must use the
colon notation explained below to specify a function from a
specific source file.
Sometimes, function names contain dots. In such cases, it is
necessary to add a leading colon to the name. For example,
`:.mul' selects function `.mul'.
In some object file formats, symbols have a leading underscore.
`gprof' will normally not print these underscores. When you name a
symbol in a symspec, you should type it exactly as `gprof' prints
it in its output. For example, if the compiler produces a symbol
`_main' from your `main' function, `gprof' still prints it as
`main' in its output, so you should use `main' in symspecs.
`main.c:main'
Selects function `main' in file `main.c'.
`main.c:134'
Selects line 134 in file `main.c'.

File: gprof.info, Node: Output, Next: Inaccuracy, Prev: Invoking, Up: Top
5 Interpreting `gprof''s Output
*******************************
`gprof' can produce several different output styles, the most important
of which are described below. The simplest output styles (file
information, execution count, and function and file ordering) are not
described here, but are documented with the respective options that
trigger them. *Note Output Options: Output Options.
* Menu:
* Flat Profile:: The flat profile shows how much time was spent
executing directly in each function.
* Call Graph:: The call graph shows which functions called which
others, and how much time each function used
when its subroutine calls are included.
* Line-by-line:: `gprof' can analyze individual source code lines
* Annotated Source:: The annotated source listing displays source code
labeled with execution counts
* Other Events:: Profiling events other than cycle counts.

File: gprof.info, Node: Flat Profile, Next: Call Graph, Up: Output
5.1 The Flat Profile
====================
The "flat profile" shows the total histogram counts for each function.
Unless the `-z' option is given, functions with no apparent counts and
no apparent calls to them, are not mentioned. Note that for hardware
profiling if a function was not compiled for profiling, and didn't run
long enough to show up on the program counter histogram, it will be
indistinguishable from a function that was never called. Also, if the
compiler optimizes a function call by inlining the function body, then
the function call will not be counted and the time spent in the inlined
function will be attributed to the caller. Line-by-line profiling may
be helpful in revealing the effects of inlined functions. *Note
Line-by-line Profiling: Line-by-line.
This is part of a flat profile for a small program:
Flat profile:
Each sample counts as 16384 cycles.
self total
cumulative self cycles cycles
% cycles cycles calls /call /call name
(K) (K) (K) (K)
66.67 49.15 49.15 7208 0.01 0.01 open
16.67 65.54 16.38 244 0.07 0.20 offtime
16.67 81.92 16.38 8 2.05 2.05 memccpy
16.67 98.30 16.38 7 2.34 2.34 write
0.00 98.30 0.00 236 0.00 0.00 tzset
0.00 98.30 0.00 192 0.00 0.00 tolower
0.00 98.30 0.00 47 0.00 0.00 strlen
0.00 98.30 0.00 45 0.00 0.00 strchr
0.00 98.30 0.00 1 0.00 98.30 main
0.00 98.30 0.00 1 0.00 0.00 memcpy
0.00 98.30 0.00 1 0.00 16.38 print
0.00 98.30 0.00 1 0.00 98.30 report
...
The functions are sorted first by decreasing run-time spent in them,
then by decreasing number of calls, then alphabetically by name.
`gprof' attempts to scale results so that the tables contain numbers
of reasonable magnitude. If the counts are scaled, the scaling factor
is shown at the top of the scaled columns. "T" indicates that the
values are in units of trillions; "G" indicates billions; "M" indicates
millions; and "K" indicates thousands.
For hardware profiling, where the profile data is sampled, you must
be careful interpreting the `gprof' results. Just before the column
headers, a statement appears indicating how many units each sample
counted as. This "sampling period" estimates the margin of error in
each of the figures. A figure that is not much larger than this is not
reliable. In this example, each sample counted as 16,384 cycles. The
program's total execution time was 98.30 Kcycles, as indicated by the
`cumulative cycles' field. Since each sample counted for 16,384
seconds, this means only six samples were taken during the run. Three
of the samples occurred while the program was in the `open' function,
as indicated by the `self cycles' field. Each of the other three
samples occurred once each in `offtime', `memccpy', and `write'. Since
only six samples were taken, none of these values can be regarded as
particularly reliable. In another run, the `self cycles' field for
`memccpy' might well be `0.00' or `32.77'. *Note Statistical Sampling
Error: Sampling Error, for a complete discussion.
The remaining functions in the listing (those whose `self cycles'
field is `0.00') didn't appear in the histogram samples at all.
However, the call graph indicated that they were called, so therefore
they are listed, sorted in decreasing order by the `calls' field.
Clearly some time was spent executing these functions, but the paucity
of histogram samples prevents any determination of how much time each
took.
Here is what the fields in each line mean (the UNITS depend on the
events being profiled, e.g., cycles, interlocks, etc.):
`%'
This is the percentage of the total histogram counts that are
attributed to this function. These should all add up to 100%.
`cumulative UNITS'
This is the cumulative total number of UNITS the computer spent
executing this function, plus the time spent in all the functions
above this one in this table.
`self UNITS'
This is the number of UNITS accounted for by this function alone.
The flat profile listing is sorted first by this number.
`calls'
This is the total number of times the function was called.
`self UNITS/call'
This represents the average number of UNITS spent in this function
per call.
`total UNITS/call'
This represents the average number of UNITS spent in this function
and its descendants per call. This is the only field in the flat
profile that uses call graph analysis.
`name'
This is the name of the function. The flat profile is sorted by
this field alphabetically after the "self UNITS" and "calls"
fields are sorted.

File: gprof.info, Node: Call Graph, Next: Line-by-line, Prev: Flat Profile, Up: Output
5.2 The Call Graph
==================
The "call graph" shows how much time was spent in each function and its
children. From this information, you can find functions that, while
they themselves may not have used much time, called other functions
that did use unusual amounts of time. Note that in the same way as the
flat profile, a function call inlined by the compiler will not be
visible in the call graph and the counts for the inlined function will
be attributed to the caller.
Here is a sample call from a small program. This call came from the
same `gprof' run as the flat profile example in the previous section.
index % self children called name
(K) (K)
<spontaneous>
[1] 100.0 0.00 98.30 _start [1]
0.00 98.30 1/1 main [2]
0.00 0.00 1/2 _atexit [28]
0.00 0.00 1/1 exit [59]
-----------------------------------------------
0.00 98.30 1/1 _start [1]
[2] 100.0 0.00 98.30 1 main [2]
0.00 98.30 1/1 report [3]
-----------------------------------------------
0.00 98.30 1/1 main [2]
[3] 100.0 0.00 98.30 1 report [3]
0.00 49.15 8/8 timelocal [6]
0.00 16.38 1/1 print [9]
0.00 16.38 9/9 fgets [12]
0.00 0.00 12/34 strncmp <cycle 1> [40]
0.00 0.00 8/8 lookup [20]
0.00 0.00 1/1 fopen [21]
0.00 0.00 8/8 chewtime [24]
0.00 0.00 8/16 skipspace [44]
-----------------------------------------------
[4] 60.5 16.38 49.15 8+472 <cycle 2 as a whole> [4]
16.38 49.15 244+260 offtime <cycle 2> [7]
0.00 0.00 236+1 tzset <cycle 2> [26]
-----------------------------------------------
As with the flat profile, `gprof' attempts to scale results so that
the tables contain numbers of reasonable magnitude. If the counts are
scaled, the scaling factor is shown at the top of the scaled columns.
"T" indicates that the values are in units of trillions; "G" indicates
billions; "M" indicates millions; and "K" indicates thousands.
The lines full of dashes divide this table into "entries", one for
each function. Each entry has one or more lines.
In each entry, the primary line is the one that starts with an index
number in square brackets. The end of this line says which function
the entry is for. The preceding lines in the entry describe the
callers of this function and the following lines describe its
subroutines (also called "children" when we speak of the call graph).
The entries are sorted by time spent in the function and its
subroutines.
* Menu:
* Primary:: Details of the primary line's contents.
* Callers:: Details of caller-lines' contents.
* Subroutines:: Details of subroutine-lines' contents.
* Cycles:: When there are cycles of recursion,
such as `a' calls `b' calls `a'...

File: gprof.info, Node: Primary, Next: Callers, Up: Call Graph
5.2.1 The Primary Line
----------------------
The "primary line" in a call graph entry is the line that describes the
function which the entry is about and gives the overall statistics for
this function.
For reference, we repeat the primary line from the entry for function
`report' in our main example, together with the heading line that shows
the names of the fields:
index % self children called name
...
[3] 100.0 0.00 98.30 1 report [3]
Here is what the fields in the primary line mean:
`index'
Entries are numbered with consecutive integers. Each function
therefore has an index number, which appears at the beginning of
its primary line.
Each cross-reference to a function, as a caller or subroutine of
another, gives its index number as well as its name. The index
number guides you if you wish to look for the entry for that
function.
`%'
This is the percentage of the total histogram counts that were
attributed to this function and to subroutines called from this
function.
The histogram hits for this function are counted again for the
callers of this function. Therefore, adding up these percentages
is meaningless.
`self'
This is the total number of histogram hits for this function. This
should be identical to the number printed in the `self' field for
this function in the flat profile.
`children'
This is the total number of histogram hits for subroutine calls
made by this function. This should be equal to the sum of all the
`self' and `children' entries of the children listed directly
below this function.
`called'
This is the number of times the function was called.
If the function called itself recursively, there are two numbers,
separated by a `+'. The first number counts non-recursive calls,
and the second counts recursive calls.
In the example above, the function `report' was called once from
`main'.
`name'
This is the name of the current function. The index number is
repeated after it.
If the function is part of a cycle of recursion, the cycle number
is printed between the function's name and the index number (*note
How Mutually Recursive Functions Are Described: Cycles.). For
example, if function `gnurr' is part of cycle number one, and has
index number twelve, its primary line would be end like this:
gnurr <cycle 1> [12]

File: gprof.info, Node: Callers, Next: Subroutines, Prev: Primary, Up: Call Graph
5.2.2 Lines for a Function's Callers
------------------------------------
A function's entry has a line for each function it was called by.
These lines' fields correspond to the fields of the primary line, but
their meanings are different because of the difference in context.
For reference, we repeat two lines from the entry for the function
`report', the primary line and one caller-line preceding it, together
with the heading line that shows the names of the fields:
index % self children called name
...
0.00 98.30 1/1 main [2]
[3] 100.0 0.00 98.30 1 report [3]
Here are the meanings of the fields in the caller-line for `report'
called from `main':
`self'
An estimate of the number of histogram hits for `report' itself
when it was called from `main'.
`children'
An estimate of the number of histogram hits for subroutines of
`report' when `report' was called from `main'.
The sum of the `self' and `children' fields is an estimate of the
number of histogram hits within calls to `report' from `main'.
`called'
Two numbers: the number of times `report' was called from `main',
followed by the total number of non-recursive calls to `report'
from all its callers.
`name and index number'
The name of the caller of `report' to which this line applies,
followed by the caller's index number.
Not all functions have entries in the call graph; some options to
`gprof' request the omission of certain functions. When a caller
has no entry of its own, it still has caller-lines in the entries
of the functions it calls.
If the caller is part of a recursion cycle, the cycle number is
printed between the name and the index number.
If the identity of the callers of a function cannot be determined, a
dummy caller-line is printed which has `<spontaneous>' as the "caller's
name" and all other fields blank. This can happen for signal handlers.

File: gprof.info, Node: Subroutines, Next: Cycles, Prev: Callers, Up: Call Graph
5.2.3 Lines for a Function's Subroutines
----------------------------------------
A function's entry has a line for each of its subroutines--in other
words, a line for each other function that it called. These lines'
fields correspond to the fields of the primary line, but their meanings
are different because of the difference in context.
For reference, we repeat two lines from the entry for the function
`main', the primary line and a line for a subroutine, together with the
heading line that shows the names of the fields:
index % self children called name
...
[2] 100.0 0.00 98.30 1 main [2]
0.00 98.30 1/1 report [3]
Here are the meanings of the fields in the subroutine-line for `main'
calling `report':
`self'
An estimate of the number of histogram hits directly within
`report' when `report' was called from `main'.
`children'
An estimate of the number of histogram hits in subroutines of
`report' when `report' was called from `main'.
The sum of the `self' and `children' fields is an estimate of the
total histogram hits in calls to `report' from `main'.
`called'
Two numbers, the number of calls to `report' from `main' followed
by the total number of non-recursive calls to `report'. This
ratio is used to determine how much of `report''s `self' and
`children' time gets credited to `main'. *Note Estimating
`children' Times: Assumptions.
`name'
The name of the subroutine of `main' to which this line applies,
followed by the subroutine's index number.
If the caller is part of a recursion cycle, the cycle number is
printed between the name and the index number.

File: gprof.info, Node: Cycles, Prev: Subroutines, Up: Call Graph
5.2.4 How Mutually Recursive Functions Are Described
----------------------------------------------------
The graph may be complicated by the presence of "cycles of recursion"
in the call graph. A cycle exists if a function calls another function
that (directly or indirectly) calls (or appears to call) the original
function. For example: if `a' calls `b', and `b' calls `a', then `a'
and `b' form a cycle.
Whenever there are call paths both ways between a pair of functions,
they belong to the same cycle. If `a' and `b' call each other and `b'
and `c' call each other, all three make one cycle. Note that even if
`b' only calls `a' if it was not called from `a', `gprof' cannot
determine this, so `a' and `b' are still considered a cycle.
The cycles are numbered with consecutive integers. When a function
belongs to a cycle, each time the function name appears in the call
graph it is followed by `<cycle NUMBER>'.
The reason cycles matter is that they make the time values in the
call graph paradoxical. The "time spent in children" of `a' should
include the time spent in its subroutine `b' and in `b''s
subroutines--but one of `b''s subroutines is `a'! How much of `a''s
time should be included in the children of `a', when `a' is indirectly
recursive?
The way `gprof' resolves this paradox is by creating a single entry
for the cycle as a whole. The primary line of this entry describes the
total time spent directly in the functions of the cycle. The
"subroutines" of the cycle are the individual functions of the cycle,
and all other functions that were called directly by them. The
"callers" of the cycle are the functions, outside the cycle, that
called functions in the cycle.
Here is an example portion of a call graph which shows a cycle
containing functions `a' and `b'. The cycle was entered by a call to
`a' from `main'; both `a' and `b' called `c'.
index % self children called name
----------------------------------------
1.77 0.00 1/1 main [2]
[3] 91.7 1.77 0.00 1+5 <cycle 1 as a whole> [3]
1.02 0.00 3 b <cycle 1> [4]
0.75 0.00 2 a <cycle 1> [5]
----------------------------------------
3 a <cycle 1> [5]
[4] 52.8 1.02 0.00 0 b <cycle 1> [4]
2 a <cycle 1> [5]
0.00 0.00 3/6 c [6]
----------------------------------------
1.77 0.00 1/1 main [2]
2 b <cycle 1> [4]
[5] 38.9 0.75 0.00 1 a <cycle 1> [5]
3 b <cycle 1> [4]
0 0.00 3/6 c [6]
----------------------------------------
(The entire call graph for this program contains in addition an entry
for `main', which calls `a', and an entry for `c', with callers `a' and
`b'.)
index % self children called name
<spontaneous>
[1] 100.0 0.00 1.93 0 start [1]
0.16 1.77 1/1 main [2]
----------------------------------------
0.16 1.77 1/1 start [1]
[2] 100.0 0.16 1.77 1 main [2]
1.77 0.00 1/1 a <cycle 1> [5]
----------------------------------------
1.77 0.00 1/1 main [2]
[3] 91.7 1.77 0.00 1+5 <cycle 1 as a whole> [3]
1.02 0.00 3 b <cycle 1> [4]
0.75 0.00 2 a <cycle 1> [5]
0.00 0.00 6/6 c [6]
----------------------------------------
3 a <cycle 1> [5]
[4] 52.8 1.02 0.00 0 b <cycle 1> [4]
2 a <cycle 1> [5]
0.00 0.00 3/6 c [6]
----------------------------------------
1.77 0.00 1/1 main [2]
2 b <cycle 1> [4]
[5] 38.9 0.75 0.00 1 a <cycle 1> [5]
3 b <cycle 1> [4]
0.00 0.00 3/6 c [6]
----------------------------------------
0.00 0.00 3/6 b <cycle 1> [4]
0.00 0.00 3/6 a <cycle 1> [5]
[6] 0.0 0.00 0.00 6 c [6]
----------------------------------------
The `self' field of the cycle's primary line is the total histogram
count for all the functions of the cycle. It equals the sum of the
`self' fields for the individual functions in the cycle, found in the
entry in the subroutine lines for these functions.
The `children' fields of the cycle's primary line and subroutine
lines count only subroutines outside the cycle. Even though `a' calls
`b', the time spent in those calls to `b' is not counted in `a''s
`children' time. Thus, we do not encounter the problem of what to do
when the time in those calls to `b' includes indirect recursive calls
back to `a'.
The `children' field of a caller-line in the cycle's entry estimates
the number of histogram hits _in the whole cycle_, and its other
subroutines, on the times when that caller called a function in the
cycle.
The `called' field in the primary line for the cycle has two numbers:
first, the number of times functions in the cycle were called by
functions outside the cycle; second, the number of times they were
called by functions in the cycle (including times when a function in
the cycle calls itself). This is a generalization of the usual split
into non-recursive and recursive calls.
The `called' field of a subroutine-line for a cycle member in the
cycle's entry says how many time that function was called from
functions in the cycle. The total of all these is the second number in
the primary line's `called' field.
In the individual entry for a function in a cycle, the other
functions in the same cycle can appear as subroutines and as callers.
These lines show how many times each function in the cycle called or
was called from each other function in the cycle. The `self' and
`children' fields in these lines are blank because of the difficulty of
defining meanings for them when recursion is going on.

File: gprof.info, Node: Line-by-line, Next: Annotated Source, Prev: Call Graph, Up: Output
5.3 Line-by-line Profiling
==========================
`gprof''s `-l' option causes the program to perform "line-by-line"
profiling. In this mode, histogram samples are assigned not to
functions, but to individual lines of source code. The program must be
compiled with a `-g' option to generate debugging symbols for tracking
source code lines.
The flat profile is the most useful output table in line-by-line
mode. The call graph isn't as useful as normal, since the current
version of `gprof' does not propagate call graph arcs from source code
lines to the enclosing function. The call graph does, however, show
each line of code that called each function, along with a count.
The `-f' option also enables line-by-line profiling. The only
difference between `-f' and `-l' is the order of the entries in the
flat profile. With `-f', the flat profile entries are grouped by
function so that all the lines for a function appear together. The
functions are shown in decreasing order of histogram counts, and the
lines within each function are also sorted in decreasing order of
histogram counts.
Here is a section of `gprof''s output, without line-by-line
profiling. Note that `ct_init' accounted for 13327 calls to
`init_block'.
Flat profile:
self total
cumulative self cycles cycles
% cycles cycles calls /call /call name
(K) (K) (K) (K)
30.77 0.13 0.04 6335 6.31 6.31 ct_init
Call graph (explanation follows)
index % self children called name
(K) (K)
0.00 0.00 1/13496 name_too_long
0.00 0.00 40/13496 deflate
0.00 0.00 128/13496 deflate_fast
0.00 0.00 13327/13496 ct_init
[7] 0.0 0.00 0.00 13496 init_block
Now let's look at some of `gprof''s output from the same program run,
this time with line-by-line profiling enabled. Note that `ct_init''s
histogram hits are broken down into four lines of source code--lines
349, 351, 382 and 385. In the call graph, note how `ct_init''s 13327
calls to `init_block' are broken down into one call from line 396, 3071
calls from line 384, 3730 calls from line 385, and 6525 calls from 387.
Flat profile:
cumulative self
% cycles cycles calls name
(K) (K)
7.69 0.10 0.01 ct_init (trees.c:349)
7.69 0.11 0.01 ct_init (trees.c:351)
7.69 0.12 0.01 ct_init (trees.c:382)
7.69 0.13 0.01 ct_init (trees.c:385)
Call graph (explanation follows)
index % self children called name
(K) (K)
0.00 0.00 1/13496 name_too_long (gzip.c:1440)
0.00 0.00 1/13496 deflate (deflate.c:763)
0.00 0.00 1/13496 ct_init (trees.c:396)
0.00 0.00 2/13496 deflate (deflate.c:727)
0.00 0.00 4/13496 deflate (deflate.c:686)
0.00 0.00 5/13496 deflate (deflate.c:675)
0.00 0.00 12/13496 deflate (deflate.c:679)
0.00 0.00 16/13496 deflate (deflate.c:730)
0.00 0.00 128/13496 deflate_fast (deflate.c:654)
0.00 0.00 3071/13496 ct_init (trees.c:384)
0.00 0.00 3730/13496 ct_init (trees.c:385)
0.00 0.00 6525/13496 ct_init (trees.c:387)
[6] 0.0 0.00 0.00 13496 init_block (trees.c:408)

File: gprof.info, Node: Annotated Source, Next: Other Events, Prev: Line-by-line, Up: Output
5.4 The Annotated Source Listing
================================
`gprof''s `-A' option triggers an annotated source listing, which lists
the program's source code, each function labeled with the number of
times it was called. You may also need to specify the `-I' option, if
`gprof' can't find the source code files.
If you use the Xtensa ISS to profile instruction counts, `gprof' can
determine how many times each basic-block of code was executed, and the
basic-block execution counts can be seen in the annotated source
listing. Run ISS with `--client_cmds="profile --instructions"' to
profile instruction counts. If you profile cycle counts (the default),
the basic-block execution counts are not available.
For example, consider the following function, taken from gzip, with
line numbers added:
1 ulg updcrc(s, n)
2 uch *s;
3 unsigned n;
4 {
5 register ulg c;
6
7 static ulg crc = (ulg)0xffffffffL;
8
9 if (s == NULL) {
10 c = 0xffffffffL;
11 } else {
12 c = crc;
13 if (n) do {
14 c = crc_32_tab[...];
15 } while (--n);
16 }
17 crc = c;
18 return c ^ 0xffffffffL;
19 }
`updcrc' has at least five basic-blocks. One is the function
itself. The `if' statement on line 9 generates two more basic-blocks,
one for each branch of the `if'. A fourth basic-block results from the
`if' on line 13, and the contents of the `do' loop form the fifth
basic-block. The compiler may also generate additional basic-blocks to
handle various special cases.
Run `xt-gprof -l -A' for line-by-line annotated source output. The
`-x' option is also helpful, to ensure that each line of code is
labeled at least once. Here is `updcrc''s annotated source listing for
a sample `gzip' run:
ulg updcrc(s, n)
uch *s;
unsigned n;
2 ->{
register ulg c;
static ulg crc = (ulg)0xffffffffL;
2 -> if (s == NULL) {
1 -> c = 0xffffffffL;
1 -> } else {
1 -> c = crc;
1 -> if (n) do {
26312 -> c = crc_32_tab[...];
26312,1,26311 -> } while (--n);
}
2 -> crc = c;
2 -> return c ^ 0xffffffffL;
2 ->}
In this example, the function was called twice, passing once through
each branch of the `if' statement. The body of the `do' loop was
executed a total of 26312 times. Note how the `while' statement is
annotated. It began execution 26312 times, once for each iteration
through the loop. One of those times (the last time) it exited, while
it branched back to the beginning of the loop 26311 times.

File: gprof.info, Node: Other Events, Prev: Annotated Source, Up: Output
5.5 Profiling Other Events
==========================
When analyzing a program's behavior, it may be helpful to profile events
other than cycle counts. The profiling client in the Xtensa ISS can
also collect information on events such as cache misses, pipeline
interlocks, etc. *Note Executing the Program: Executing. All the
features of `gprof' can be used to analyze the profile data, regardless
of the kind of events being profiled. The only change is that the
histogram counts in the profile data file represent the occurrence of
these other events for each instruction.
For example, here is an excerpt of the flat profile output when the
ISS was used to profile instruction cache misses in a small program:
Flat profile:
self total
cumulative self icmisses icmisses
% icmisses icmisses calls /call /call name
28.12 591.00 591.00 296 2.00 2.00 memcpy
12.32 850.00 259.00 86 3.01 3.01 check_range
7.66 1011.00 161.00 117 1.38 1.39 call
6.37 1145.00 134.00 133 1.01 6.60 exec
5.47 1260.00 115.00 38 3.03 3.25 _write_r
5.14 1368.00 108.00 38 2.84 2.84 memchr

File: gprof.info, Node: Inaccuracy, Next: GNU Free Documentation License, Prev: Output, Up: Top
6 Inaccuracy of `gprof' Output
******************************
* Menu:
* Sampling Error:: Statistical margins of error
* Assumptions:: Estimating children times

File: gprof.info, Node: Sampling Error, Next: Assumptions, Up: Inaccuracy
6.1 Statistical Sampling Error
==============================
This section does not apply when profiling with the Xtensa ISS. The
ISS collects profile data continuously--there is no sampling involved.
For hardware profiling, you can control the sampling errors to some
extent by adjusting the sampling frequency with the
`xt_profile_set_frequency' function. See the `Xtensa Software
Development Toolkit User's Guide' for more information on hardware
profiling.
The run-time figures that `gprof' gives you are based on a sampling
process, so they are subject to statistical inaccuracy. If a function
runs only a small amount of time, so that on the average the sampling
process ought to catch that function in the act only once, there is a
pretty good chance it will actually find that function zero times, or
twice.
By contrast, the number-of-calls and basic-block figures are derived
by counting, not sampling. They are completely accurate and will not
vary from run to run if your program is deterministic and single
threaded. In multi-threaded applications, or single threaded
applications that link with multi-threaded libraries, the counts are
only deterministic if the counting function is thread-safe. (Note:
beware that the mcount counting function in glibc is _not_ thread-safe).
The "sampling period" that is printed at the beginning of the flat
profile says how often samples are taken. The rule of thumb is that a
run-time figure is accurate if it is considerably bigger than the
sampling period.
The actual amount of error can be predicted. For N samples, the
_expected_ error is the square-root of N. For example, if the sampling
period is 0.01 seconds and `foo''s run-time is 1 second, N is 100
samples (1 second/0.01 seconds), sqrt(N) is 10 samples, so the expected
error in `foo''s run-time is 0.1 seconds (10*0.01 seconds), or ten
percent of the observed value. Again, if the sampling period is 0.01
seconds and `bar''s run-time is 100 seconds, N is 10000 samples,
sqrt(N) is 100 samples, so the expected error in `bar''s run-time is 1
second, or one percent of the observed value. It is likely to vary
this much _on the average_ from one profiling run to the next.
(_Sometimes_ it will vary more.)
This does not mean that a small run-time figure is devoid of
information. If the program's _total_ run-time is large, a small
run-time for one function does tell you that that function used an
insignificant fraction of the whole program's time. Usually this means
it is not worth optimizing.
One way to get more accuracy is to give your program more (but
similar) input data so it will take longer. Another way is to combine
the data from several runs, using the `-s' option of `gprof'. Here is
how:
1. Run your program once.
2. Issue the command `mv gmon.out gmon.sum'.
3. Run your program again, the same as before.
4. Merge the new data in `gmon.out' into `gmon.sum' with this command:
xt-gprof -s EXECUTABLE-FILE gmon.out gmon.sum
5. Repeat the last two steps as often as you wish.
6. Analyze the cumulative data using this command:
xtgprof EXECUTABLE-FILE gmon.sum > OUTPUT-FILE

File: gprof.info, Node: Assumptions, Prev: Sampling Error, Up: Inaccuracy
6.2 Estimating `children' Times
===============================
Some of the figures in the call graph are estimates--for example, the
`children' time values and all the time figures in caller and
subroutine lines.
There is no direct information about these measurements in the
profile data itself. Instead, `gprof' estimates them by making an
assumption about your program that might or might not be true.
The assumption made is that the average time spent in each call to
any function `foo' is not correlated with who called `foo'. If `foo'
used 5 seconds in all, and 2/5 of the calls to `foo' came from `a',
then `foo' contributes 2 seconds to `a''s `children' time, by
assumption.
This assumption is usually true enough, but for some programs it is
far from true. Suppose that `foo' returns very quickly when its
argument is zero; suppose that `a' always passes zero as an argument,
while other callers of `foo' pass other arguments. In this program,
all the time spent in `foo' is in the calls from callers other than `a'.
But `gprof' has no way of knowing this; it will blindly and incorrectly
charge 2 seconds of time in `foo' to the children of `a'.

File: gprof.info, Node: GNU Free Documentation License, Next: History, Prev: Inaccuracy, Up: Top
Appendix A GNU Free Documentation License
*****************************************
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
`http://fsf.org/'
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
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being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book.
We recommend this License principally for works whose purpose is
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Permission is granted to copy, distribute and/or modify this document
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File: gprof.info, Node: History, Prev: GNU Free Documentation License, Up: Top
Appendix B History
******************
The original version of this document, entitled "GNU gprof, the GNU
Profiler", was written by Jay Fenlason and Richard Stallman. The
version for `gprof' 2.18 was released in 2007 and published by the Free
Software Foundation.
Tensilica, Inc. changed the title to "GNU Profiler User's Guide" and
modified the document to include features specific to Xtensa processors.
The revised document was published by Tensilica, Inc. on the date shown
in the inside cover page. The TeXinfo source files for this modified
document are available from `http://www.tensilica.com/gnudocs'.

Tag Table:
Node: Top1998
Node: Revisions3144
Node: Introduction3440
Node: Compiling8542
Node: Executing11630
Node: Xtensa ISS12414
Node: Xtensa Hardware15019
Node: Invoking15808
Node: Output Options17093
Node: Analysis Options24281
Node: Miscellaneous Options29200
Node: Symspecs30403
Node: Output32232
Node: Flat Profile33339
Node: Call Graph38541
Node: Primary42141
Node: Callers44735
Node: Subroutines46868
Node: Cycles48723
Node: Line-by-line55660
Node: Annotated Source59795
Node: Other Events62848
Node: Inaccuracy64285
Node: Sampling Error64564
Node: Assumptions67823
Node: GNU Free Documentation License69078
Node: History94243

End Tag Table
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