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170 lines
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HTML
170 lines
7.0 KiB
HTML
<html>
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<head><title>The Jprof Profiler</title></head><body>
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<center><h1>The Jprof Profiler</h1></center><hr>
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<h2>Introduction</h2>
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Jprof is a profiling tool. I am writing it because I need to find out
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where mozilla is spending its time, and there do not seem to be any
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profilers for Linux that can handle threads and/or shared libraries.
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This code is based heavily on Kipp Hickman's leaky.
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<P> <h2>Operation</h2>
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Jprof operates by installing a timer which periodically interrupts mozilla.
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When this timer goes off, the jprof code inside mozilla walks the function
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call stack to determine which code was executing. By collecting a large
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number of these call stacks, it is possible to deduce where mozilla is
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spending its time.
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<P> <h2>Use</h2>
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First, check out the jprof source code since it is not a part of the
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default SeaMonkeyAll CVS tag. To do this do:
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<pre>
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cvs co mozilla/tools/jprof
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<pre>
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<P>
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Next, enable jprof and rebuild mozilla:
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<P>
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<pre>
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configure --enable-jprof
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make
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</pre>
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Now you can run jprof. To do this the JPROF_FLAGS environment variable
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must be set. As a simple example:
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<pre>
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cd dist/bin
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env JPROF_FLAGS=JP_START LD_LIBRARY_PATH=. ./mozilla-bin
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</pre>
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<P>
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The JPROF_FLAGS environment variable can be composed of several substrings
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which have the following meanings:
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<ul>
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<li> JP_START : Install the signal handler, and start sending the
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timer signals.
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<li> JP_DEFER : Install the signal handler, but don't start sending
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the timer signals. The user must start the signals by sending
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the first one (with <code>kill -PROF</code>, or with <code>kill
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-ALRM</code> if JP_REALTIME is used).
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<li> JP_FIRST=x : Wait x seconds before starting the timer
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<li> JP_PERIOD=y : Set timer to interrupt every y seconds
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<li> JP_REALTIME : Do the profiling in intervals of real time rather
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than intervals of time used by the mozilla process (and the kernel
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when doing work for mozilla). This could probably lead to weird
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results (you'll see whatever runs when mozilla is waiting for events),
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but is needed to see time spent in the X server.
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</ul>
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For example you could say:
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<pre>
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setenv JPROF_FLAGS "JP_START JP_FIRST=3 JP_PERIOD=0.025"
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</pre>
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<P>
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When mozilla runs with jprof enabled, it writes to a file called jprof-log
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for each timer signal and it writes to jprof-map when it exits.
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Sending a SIGUSR1 to mozilla (<code>kill -USR1</code>) will cause the
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timer signals to stop and jprof-map to be written, but it will not
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close jprof-log.
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Combining SIGUSR1 with the JP_DEFER option allows profiling of one
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sequence of actions.
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(After a SIGUSR1, sending another timer signal (SIGPROF or SIGALRM)
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could be used to continue writing data to the same output, although this
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has not been tested.)
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<p>
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The jprof executable is used to turn these
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files into readable output. To do this jprof needs the name of the mozilla
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binary and the log file. It deduces the name of the map file:
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<pre>
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./jprof mozilla-bin ./jprof-log > tmp.html
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</pre>
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This will generate the file tmp.html which you should view in a web browser.
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<P> <h2>Interpretation</h2>
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The Jprof output is split into a flat portion and a hierarchical portion.
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There are links to each section at the top of the page. It is typically
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easier to analyze the profile by starting with the flat output and following
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the links contained in the flat output up to the hierarchical output.
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<P> <h3>Flat output</h3>
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The flat portion of the profile indicates which functions were executing
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when the timer was going off. It is displayed as a list of functions names
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on the right and the number of times that function was interrupted on the
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left. The list is sorted by decreasing interrupt count. For example:
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<blockquote> <pre>
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Count Function Name
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36 <A href="#175458">_init</a>
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30 <A href="#186088">SelectorMatches(nsIPresContext *, nsCSSSelector *, nsIContent *, int)</a>
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22 <A href="#101380">_init</a>
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22 <A href="#1991">_dl_lookup_symbol</a>
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</pre> </blockquote>
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In general, the functions with the highest count are the functions which
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are taking the most time.
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<P>
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The function names are linked to the entry for that function in the
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hierarchical profile, which is described in the next section.
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<P> <h3>Hierarchical output</h3>
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The hierarchical output is divided up into sections, with each section
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corresponding to one function. A typical section looks something like
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this:
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<blockquote><pre>
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639 <A href="#76801">nsWidget::OnMotionNotifySignal(_GdkEventMotion *)</A>
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11 <A href="#76810">nsWidget::OnButtonReleaseSignal(_GdkEventButton *)</A>
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2 <A href="#76809">nsWidget::OnButtonPressSignal(_GdkEventButton *)</A>
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76787 0 652 <A name=76787>nsWidget::DispatchMouseEvent(nsMouseEvent &)</a>
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652 <A href="#76779">nsWidget::DispatchWindowEvent(nsGUIEvent *)</A>
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</pre></blockquote>
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This block corresponds to the function nsWidget::DispatchMouseEvent.
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You can determine this because it is preceded by three numbers while
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the other function names are preceded by only one number. These three
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numbers have the following meaning. The number on the left (76787)
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is the index number, and is not important. The center number (0)
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is the number of times this function was interrupted by the timer.
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The last number (652) is the number of times this function was in the
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call stack when the timer went off. For our example we can see that
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our function was in the call stack for 652 interrupt ticks, but we were
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never the function that was running when the interrupt arrived.
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<P>
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The functions listed above the line for nsWidget::DispatchMouseEvent, are
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the functions which are calling this function. The numbers to the left of
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these function names are the number of times these functions were in the
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call stack as callers of nsWidget::DispatchMouseEvent. In our example,
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we were called 11 times by the function nsWidget::OnButtonReleaseSignal.
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<P>
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The functions listed below the list for nsWidget::DispatchMouseEvent,
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are the functions this function was calling when the timer went off.
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The numbers to the left of the function names are the number of times
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it was in the call stack as a callee of our function when the timer
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went off. In our example, each of the 652 times the timer went off
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and nsWidget::DispatchMouseEvent was in the call stack it was calling
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nsWidget::DispatchWindowEvent.
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<P> <h2>Bugs</h2>
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Currently jprof has only been tested under Red Hat Linux 6.1. It is known
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to not work under Red Hat Linux 6.0. The way I determine the stack trace
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from inside the signal handler is tightly bound to the version of glibc
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that is running. If you know of a more portable way to get this information
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please let me know.
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<P> <h3>Update</h3>
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Ben Bucksch reports that installing the Red Hat 6.1 glibc rpms on a Red Hat
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6.0 system allows jprof to work, and does not seem to break anything except
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gdm (the Gnome login program), and that can be fixed by installing the RH 6.1
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gdb rpm.
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<h3>Update</h3>
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David Baron reports that jprof works under RedHat 6.0 if one uncomments
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the <code>#define JPROF_PTHREAD_HACK</code> near the beginning of
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<code>libmalloc.cpp</code>.
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