Documentation covering profiling Cygwin programs.
This commit is contained in:
Mark Geisert
Corinna Vinschen
parent
bf81f082cd
commit
d0cf3b7c02
|
|
@ -0,0 +1,250 @@
|
|||
<?xml version="1.0" encoding='UTF-8'?>
|
||||
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
|
||||
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
|
||||
|
||||
<sect1 id="gprof"><title>Profiling Cygwin Programs</title>
|
||||
|
||||
<sect2 id="gprof-intro"><title>Introduction</title>
|
||||
<para>Profiling is a way to analyze your program to find out where it is
|
||||
spending its time. You might need to do this if it seems your program is
|
||||
taking more time to do its job than you think it should. It is always
|
||||
preferable to profile your program than to just guess where the time is
|
||||
being spent; even expert programmers are known to guess badly at this.
|
||||
</para>
|
||||
|
||||
<para>In Cygwin, you enable profiling with a compiler flag and you display
|
||||
the resulting profiling data with gprof. Read on to find out how.
|
||||
</para>
|
||||
|
||||
<para>To enable profiling of your program, first compile it with an
|
||||
additional gcc flag: <userinput>-pg</userinput>. That flag should be used
|
||||
when compiling every source file of the program. If your program has a
|
||||
Makefile, you would add the flag to all gcc compilation commands or to the
|
||||
CFLAGS= setting. A manual compilation that enables profiling looks like this:
|
||||
</para>
|
||||
|
||||
<screen>
|
||||
<prompt>bash$</prompt> <userinput>gcc -pg -g -o myapp myapp.c</userinput>
|
||||
</screen>
|
||||
|
||||
<para>The <userinput>-pg</userinput> flag causes gcc to do two additional
|
||||
things as it compiles your program. First, a small bit of code is added to
|
||||
the beginning of each function that records its address and the address it
|
||||
was called from at run time. gprof uses this data to generate a call graph.
|
||||
Second, gcc arranges to have a special "front end" added to the beginning
|
||||
of your program. The front end starts a recurring timer and every time the
|
||||
timer fires, 100 times per second, the currently executing address is saved.
|
||||
gprof uses this data to generate a "flat profile" showing where your
|
||||
program is spending its time.
|
||||
</para>
|
||||
|
||||
<para>After compiling your program (and linking it, if you do that as a
|
||||
separate step), you are ready to profile it. Just run it as you normally
|
||||
would. If there are specific code paths you want to profile, take the
|
||||
actions that would exercise those code paths. When your program exits,
|
||||
you will have an additional file in the current directory: gmon.out.
|
||||
That file contains the profiling data gprof processes and displays.
|
||||
</para>
|
||||
|
||||
<para>gprof has many flags to control its operation. The
|
||||
<citation>gprof man page</citation> details everything gprof can do. We
|
||||
will only use a few of gprof's flags here. You launch gprof as follows:
|
||||
<screen>
|
||||
<prompt>bash$</prompt> <userinput>gprof [flags] appname [datafile]...</userinput>
|
||||
</screen>
|
||||
If you don't specify any flags, gprof operates as if you gave it flags
|
||||
<userinput>-p -q</userinput> which means: generate a flat profile with
|
||||
descriptive text and generate a call graph with more descriptive text. In
|
||||
the examples below we will give specific flags to gprof to demonstrate
|
||||
specific displays. We'll also use flag <userinput>-b</userinput> which
|
||||
means: be brief, i.e. don't display the descriptive text. You can also
|
||||
specify a trailing list of one or more profiling data files. If you don't,
|
||||
gprof assumes gmon.out is the only file to process and display.
|
||||
</para>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="gprof-ex"><title>Examples</title>
|
||||
<example id="gprof-flat"><title>Flat profile</title>
|
||||
<screen>
|
||||
<prompt>bash$</prompt> <userinput>gprof -b -p myapp</userinput>
|
||||
<literal>Flat profile:
|
||||
|
||||
Each sample counts as 0.01 seconds.
|
||||
% cumulative self self total
|
||||
time seconds seconds calls s/call s/call name
|
||||
25.11 13.34 13.34 1 13.34 13.34 func0
|
||||
25.00 26.62 13.28 1 13.28 13.28 func1
|
||||
25.00 39.90 13.28 1 13.28 13.28 func3
|
||||
24.89 53.12 13.22 1 13.22 13.22 func2
|
||||
</literal> </screen> </example>
|
||||
|
||||
<example id="gprof-cg"><title>Call graph</title>
|
||||
<screen>
|
||||
<prompt>bash$</prompt> <userinput>gprof -b -q myapp</userinput>
|
||||
<literal> Call graph
|
||||
|
||||
|
||||
granularity: each sample hit covers 4 byte(s) for 0.02% of 53.12 seconds
|
||||
|
||||
index % time self children called name
|
||||
<spontaneous>
|
||||
[1] 100.0 0.00 53.12 main [1]
|
||||
13.34 0.00 1/1 func0 [2]
|
||||
13.28 0.00 1/1 func1 [3]
|
||||
13.28 0.00 1/1 func3 [4]
|
||||
13.22 0.00 1/1 func2 [5]
|
||||
-----------------------------------------------
|
||||
13.34 0.00 1/1 main [1]
|
||||
[2] 25.1 13.34 0.00 1 func0 [2]
|
||||
-----------------------------------------------
|
||||
13.28 0.00 1/1 main [1]
|
||||
[3] 25.0 13.28 0.00 1 func1 [3]
|
||||
-----------------------------------------------
|
||||
13.28 0.00 1/1 main [1]
|
||||
[4] 25.0 13.28 0.00 1 func3 [4]
|
||||
-----------------------------------------------
|
||||
13.22 0.00 1/1 main [1]
|
||||
[5] 24.9 13.22 0.00 1 func2 [5]
|
||||
-----------------------------------------------
|
||||
|
||||
|
||||
Index by function name
|
||||
|
||||
[2] func0 [5] func2
|
||||
[3] func1 [4] func3
|
||||
</literal> </screen> </example>
|
||||
|
||||
<example id="gprof-line"><title>Source line profile</title>
|
||||
<screen>
|
||||
<prompt>bash$</prompt> <userinput>gprof -b -l myapp</userinput>
|
||||
<literal>Flat profile:
|
||||
|
||||
Each sample counts as 0.01 seconds.
|
||||
% cumulative self self total
|
||||
time seconds seconds calls s/call s/call name
|
||||
25.11 13.34 13.34 1 13.34 13.34 func0 (myapp.c:9 @ 1004010e0)
|
||||
25.00 26.62 13.28 1 13.28 13.28 func1 (myapp.c:10 @ 10040111a)
|
||||
25.00 39.90 13.28 1 13.28 13.28 func3 (myapp.c:12 @ 10040118e)
|
||||
24.89 53.12 13.22 1 13.22 13.22 func2 (myapp.c:11 @ 100401154)
|
||||
|
||||
|
||||
Call graph
|
||||
|
||||
|
||||
granularity: each sample hit covers 4 byte(s) for 0.02% of 53.12 seconds
|
||||
|
||||
index % time self children called name
|
||||
13.34 0.00 1/1 main (myapp.c:26 @ 10040123c) [1]
|
||||
[2] 25.1 13.34 0.00 1 func0 (myapp.c:9 @ 1004010e0) [2]
|
||||
-----------------------------------------------
|
||||
13.28 0.00 1/1 main (myapp.c:26 @ 10040123c) [1]
|
||||
[3] 25.0 13.28 0.00 1 func1 (myapp.c:10 @ 10040111a) [3]
|
||||
-----------------------------------------------
|
||||
13.28 0.00 1/1 main (myapp.c:28 @ 100401246) [5]
|
||||
[4] 25.0 13.28 0.00 1 func3 (myapp.c:12 @ 10040118e) [4]
|
||||
-----------------------------------------------
|
||||
13.22 0.00 1/1 main (myapp.c:27 @ 100401241) [7]
|
||||
[6] 24.9 13.22 0.00 1 func2 (myapp.c:11 @ 100401154) [6]
|
||||
-----------------------------------------------
|
||||
|
||||
|
||||
Index by function name
|
||||
|
||||
[2] func0 (myapp.c:9 @ 1004010e0) [6] func2 (myapp.c:11 @ 100401154)
|
||||
[3] func1 (myapp.c:10 @ 10040111a) [4] func3 (myapp.c:12 @ 10040118e)
|
||||
</literal> </screen> </example>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="gprof-ss"><title>Special situations</title>
|
||||
<sect3 id="gprof-mt"><title>Profiling multi-threaded programs</title>
|
||||
<para>Multi-threaded programs are profiled just like single-threaded programs.
|
||||
There is no mechanism to turn profiling on or off for specific threads.
|
||||
gprof combines the data for all threads when generating its displays.
|
||||
</para>
|
||||
</sect3>
|
||||
|
||||
<sect3 id="gprof-fork"><title>Profiling programs that fork</title>
|
||||
<para>Programs that fork, i.e., use the fork() system call with or without
|
||||
using exec() afterwards, require special care. Since there is only one
|
||||
gmon.out file, profiling data from the parent process might get overwritten
|
||||
by the child process, or vice-versa, after a fork(). You can avoid this by
|
||||
setting the environment variable GMON_OUT_PREFIX before running your
|
||||
program. If the variable is non-empty, its contents will be used as a
|
||||
prefix to name the profiling data files. Here's an example:
|
||||
</para>
|
||||
|
||||
<example id="gprof-prefix">
|
||||
<screen>
|
||||
<prompt>bash$</prompt> <userinput>export GMON_OUT_PREFIX=myapp.out</userinput>
|
||||
<prompt>bash$</prompt> <userinput>./myapp -fork</userinput>
|
||||
<prompt>bash$</prompt> <userinput>ls myapp.out*</userinput>
|
||||
<literal>myapp.out.2728 myapp.out.3224
|
||||
</literal>
|
||||
<prompt>bash$</prompt> <userinput>gprof -bp myapp myapp.out.2728</userinput>
|
||||
<literal>Flat profile:
|
||||
|
||||
Each sample counts as 0.01 seconds.
|
||||
% cumulative self self total
|
||||
time seconds seconds calls s/call s/call name
|
||||
50.25 30.28 30.28 2 15.14 15.14 func3
|
||||
24.99 45.34 15.06 1 15.06 15.06 func1
|
||||
24.76 60.26 14.92 1 14.92 14.92 func2
|
||||
</literal>
|
||||
<prompt>bash$</prompt> <userinput>gprof -bp myapp myapp.out.3224</userinput>
|
||||
<literal>Flat profile:
|
||||
|
||||
Each sample counts as 0.01 seconds.
|
||||
% cumulative self self total
|
||||
time seconds seconds calls s/call s/call name
|
||||
49.25 29.36 29.36 2 14.68 14.68 func3
|
||||
25.43 44.52 15.16 1 15.16 15.16 func1
|
||||
25.33 59.62 15.10 1 15.10 15.10 func2
|
||||
</literal>
|
||||
<prompt>bash$</prompt> <userinput>gprof -bp myapp myapp.out*</userinput>
|
||||
<literal>Flat profile:
|
||||
|
||||
Each sample counts as 0.01 seconds.
|
||||
% cumulative self self total
|
||||
time seconds seconds calls s/call s/call name
|
||||
49.75 59.64 59.64 4 14.91 14.91 func3
|
||||
25.21 89.86 30.22 2 15.11 15.11 func1
|
||||
25.04 119.88 30.02 2 15.01 15.01 func2
|
||||
</literal> </screen> </example>
|
||||
<para>As the last gprof command above shows, gprof can combine the data
|
||||
from a selection of profiling data files to generate its displays. Just
|
||||
list the names of those files at the end of the gprof command; you can use
|
||||
a wildcard here. NOTE: If you update your program, remember to remove stale
|
||||
profiling data files before profiling your program again. If you aren't
|
||||
careful about this, gprof could combine data from your most recent version
|
||||
with stale data from prior versions, possibly giving misleading displays.
|
||||
</para>
|
||||
</sect3>
|
||||
|
||||
<sect3 id="gprof-res"><title>Getting better profiling resolution</title>
|
||||
<para>To get better resolution (i.e., more data points) when profiling
|
||||
your program, try running it multiple times with the environment variable
|
||||
GMON_OUT_PREFIX set, as described in the previous situation. There will be
|
||||
multiple profiling data files generated and you can have gprof combine
|
||||
the data from all of them into one display.
|
||||
</para>
|
||||
</sect3>
|
||||
|
||||
<sect3 id="gprof-lib"><title>Profiling programs with their libraries</title>
|
||||
<para>At the time of this writing Cygwin's profiling support only allows
|
||||
for one range of addresses per program. It is hard-wired to be the range
|
||||
covering the .text segment of your program, which is where your code resides.
|
||||
If you build your program with static libraries (e.g., libfoo.a), the code
|
||||
from those libraries is linked into your program's .text segment so will be
|
||||
included when profiling. But dynamic libraries (e.g., libfoo.dll) reside in
|
||||
other address ranges and code within them won't be included.
|
||||
</para>
|
||||
</sect3>
|
||||
|
||||
<sect3 id="gprof-cyg"><title>Profiling Cygwin itself</title>
|
||||
<para>Due to the issue mentioned in the previous situation and other issues,
|
||||
at the time of this writing there is no support for profiling Cygwin itself.
|
||||
</para>
|
||||
</sect3>
|
||||
</sect2>
|
||||
|
||||
</sect1>
|
||||
|
|
@ -9,4 +9,5 @@
|
|||
<xi:include href="gdb.xml"/>
|
||||
<xi:include href="dll.xml"/>
|
||||
<xi:include href="windres.xml"/>
|
||||
<xi:include href="gprof.xml"/>
|
||||
</chapter>
|
||||
|
|
|
|||
|
|
@ -71,9 +71,16 @@ first starts. Most Cygwin applications do not make use of the
|
|||
<function>dlopen ()</function> call and do not need this variable.
|
||||
</para>
|
||||
|
||||
<para>The <envar>GMON_OUT_PREFIX</envar> environment variable is helpful
|
||||
in some situations when profiling Cygwin programs. For more information,
|
||||
see <xref linkend="gprof-fork"></xref>. Only software developers with a
|
||||
need to profile their programs have a use for this variable.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
In addition to <envar>PATH</envar>, <envar>HOME</envar>,
|
||||
and <envar>LD_LIBRARY_PATH</envar>, there are three other environment
|
||||
<envar>LD_LIBRARY_PATH</envar>, and <envar>GMON_OUT_PREFIX</envar>,
|
||||
there are three other environment
|
||||
variables which, if they exist in the Windows environment, are
|
||||
converted to UNIX format: <envar>TMPDIR</envar>, <envar>TMP</envar>,
|
||||
and <envar>TEMP</envar>. The first is not set by default in the
|
||||
|
|
|
|||
Loading…
Reference in New Issue