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<!-- This Source Code Form is subject to the terms of the Mozilla Public
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<html>
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<head><title>The Jprof Profiler</title></head>
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<body bgcolor="#FFFFFF" text="#000000"
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link="#0000EE" vlink="#551A8B" alink="#FF0000">
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<center>
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<h1>The Jprof Profiler</h1>
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<font size="-1">
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<a href="mailto:jim_nance%yahoo.com">jim_nance@yahoo.com</a><p>
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Recent (4/2011) updates Randell Jesup (see bugzilla for contact info)
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</font>
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<hr>
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<a href="#introduction">Introduction</a> | <a href="#operation">Operation</a> |
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<a href="#setup">Setup</a> | <a href="#usage">Usage</a> |
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<a href="#interpretation">Interpretation</a>
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</center>
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<hr>
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<h3><a name="introduction">Introduction</a></h3>
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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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<h3><a name="operation">Operation</a></h3>
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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 call
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stack to determine which code was executing and saves the results into the
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<code>jprof-log</code> and <code>jprof-map</code> files. By collecting a large
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number of these call stacks, it is possible to deduce where mozilla is spending
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its time.
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<h3><a name="setup">Setup</a></h3>
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<p>Configure your mozilla with jprof support by adding
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<code>--enable-jprof</code> to your configure options (eg adding
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<code>ac_add_options --enable-jprof</code> to your <code>.mozconfig</code>) and
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making sure that you do <strong>not</strong> have the
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<code>--enable-strip</code> configure option set -- jprof needs symbols to
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operate. On many architectures with GCC, you'll need to add
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<code>--enable-optimize="-O3 -fno-omit-frame-pointer"</code> or the
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equivalent to ensure frame pointer generation in the compiler you're using.</p>
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<p>Finally, build mozilla with your new configuration. Now you can run jprof.</p>
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<h3><a name="usage">Usage</a></h3>
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<pre> jprof [-v] [-t] [-e exclude] [-i include] [-s stackdepth] [--last] [--all] [--start n [--end m]] [--output-dir dir] prog log [log2 ...]</pre>
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Options:
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<ul>
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<li><b>-s depth</b> : Limit depth looked at from captured stack
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frames</li>
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<li><b>-v</b> : Output some information about the symbols, memory map, etc.</li>
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<li><b>-t or --threads</b> : Group output according to thread. May require external
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LD_PRELOAD library to help force sampling of spawned threads; jprof
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may capture the main thread only. See <a
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href="http://sam.zoy.org/writings/programming/gprof.html">gprof-helper</a>;
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it may need adaption for jprof.</li>
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<li><b>--only-thread id</b> : Only output data for thread 'id'</li>
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<li><b>-e exclusion</b> : Allows excluding specific stack frames</li>
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<li><b>-i inclusion</b> : Allows including specific stack frames</li>
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<li><b>--last</b> : Only process data from the last 'section' of sampling
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(starting at the last PROF)</li>
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<li><b>--start N</b> : Start processing data at 'section' N </li>
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<li><b>--end N</b> : Stop processing data at 'section' N </li>
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<li><b>--output-dir dir</b> : Store generated .html files in the given directory </li>
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</ul>
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The behavior of jprof is determined by the value of the JPROF_FLAGS environment
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variable. This 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> <b>JP_START</b> : Install the signal handler, and start sending the
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timer signals.
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<li> <b>JP_DEFER</b> : Install the signal handler, but don't start sending
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the timer signals. The user must start the signals by sending the first
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one (with <code>kill -PROF</code>, or with <code>kill -ALRM</code> if
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JP_REALTIME is used, or with <code>kill -POLL</code> (also known as <code>kill -IO</code>) if JP_RTC_HZ is used).
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<li> <b>JP_FIRST=x</b> : Wait x seconds before starting the timer
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<li> <b>JP_PERIOD=y</b> : Set timer to interrupt every y seconds. Only
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values of y greater than or equal to 0.001 are supported. Default is
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0.050 (50ms).
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<li> <b>JP_REALTIME</b> : 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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<li> <b>JP_RTC_HZ=freq</b> : This option, only available on Linux if the
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kernel is built with RTC support, makes jprof use the RTC timer instead of
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using its own timer. This option, like JP_REALTIME, uses intervals of real
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time. This option overrides JP_PERIOD. <code>freq</code> is the frequency
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at which the timer should fire, measured in Hz. It must be a power of 2.
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The maximal frequency allowed by the kernel can be changed by writing to
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<code>/proc/sys/dev/rtc/max-user-freq</code>; the maximum value it can be
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set to is 8192. Note that <code>/dev/rtc</code> will need to be readable
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by the Firefox process; making that file world-readable is a simple way to
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accomplish that.
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<li> <b>JP_CIRCULAR=size</b> : This tells jprof to store samples in a
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circular buffer of the given size, which then will be saved (appended)
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to disk when SIGUSR1 is received or JProfStopProfiling is done. If the
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buffer overflows, the oldest entries will be evicted until there's
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space for the new entry.<p>
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SIGUSR2 will cause the circular buffer to be cleared.
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<li> <b>JP_FILENAME=basefilename</b> : This is the filename used for
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saving the log files to; the default is "jprof-log". If Electrolysis
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is used, each process after the first will have the process ID
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added ("jprof-log-3212");
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</ul>
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<h4>Starting and stopping jprof from JavaScript</h4>
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<p>
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A build with jprof enabled adds four functions to the Window object:<p>
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<code>JProfStartProfiling()</code> and <code>JProfStopProfiling()</code>: When used with JP_DEFER, these
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allow one to start and stop the timer just around whatever critical section is
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being profiled.</p><p>
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<code>JProfClearCircular()</code> and <code>JProfSaveCircular()</code>:
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These clear the circular buffer and save the buffer (without stopping), respectively.</p>
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<h4>Examples of JPROF_FLAGS usage</h4>
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<ul>
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<li>To make the timer start firing 3 seconds after the program is started and
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fire every 25 milliseconds of program time use:
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<pre>
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setenv JPROF_FLAGS "JP_START JP_FIRST=3 JP_PERIOD=0.025" </pre>
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<li>To make the timer start on your signal and fire every 1 millisecond of
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program time use:
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<pre>
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setenv JPROF_FLAGS "JP_DEFER JP_PERIOD=0.001" </pre>
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<li>To make the timer start on your signal and fire every 10 milliseconds of
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wall-clock time use:
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<pre>
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setenv JPROF_FLAGS "JP_DEFER JP_PERIOD=0.010 JP_REALTIME" </pre>
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<li>To make the timer start on your signal and fire at 8192 Hz in wall-clock
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time use:
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<pre>
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setenv JPROF_FLAGS "JP_DEFER JP_RTC_HZ=8192" </pre>
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<li>To make the timer start on JProfStartProfiling() and run continously
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with a 1ms sample rate until told to stop, then save the last 1MB of
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data:
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<pre>
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setenv JPROF_FLAGS "JP_DEFER JP_CIRCULAR=1048576 JP_PERIOD=0.001" </pre>
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</ul>
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<h4>Pausing profiles</h4>
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<P>jprof can be paused at any time by sending a SIGUSR1 to mozilla (<code>kill
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-USR1</code>). This will cause the timer signals to stop and jprof-map to be
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written, but it will not close jprof-log. Combining SIGUSR1 with the JP_DEFER
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option allows profiling of one sequence of actions by starting the timer right
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before starting the actions and stopping the timer right afterward.
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<P>After a SIGUSR1, sending another timer signal (SIGPROF, SIGALRM, or SIGPOLL (aka SIGIO),
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depending on the mode) can be used to continue writing data to the same
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output.
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<P>SIGUSR2 will cause the circular buffer to be cleared, if it's in use.
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This is useful right before running a test when you're using a large,
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continuous circular buffer, or programmatically at the start of an action
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which might take too long (JProfClearCircular()).
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<h4>Looking at the results</h4>
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Now that we have <code>jprof-log</code> and <code>jprof-map</code> files, we
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can use the jprof executable is used to turn them into readable output. To do
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this jprof needs the name of the mozilla binary and the log file. It deduces
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the name of the map file:
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<pre>
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./jprof /home/user/mozilla/objdir/dist/bin/firefox ./jprof-log > tmp.html
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</pre>
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This will generate the file <code>tmp.html</code> which you should view in a
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web browser.
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<pre>
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./jprof --output-dir=/tmp /home/user/mozilla/objdir/dist/bin/firefox ./jprof-log*
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</pre>
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This will generate a set of files in /tmp for each process.
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<h3><a name="interpretation">Interpretation</a></h3>
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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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<h4><a name="flat">Flat output</a></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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Total hit count: 151603
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Count %Total Function Name
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<a href="#23081">8806 5.8 __libc_poll</a>
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<a href="#40008">2254 1.5 __i686.get_pc_thunk.bx</a>
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<a href="#21390">2053 1.4 _int_malloc</a>
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<a href="#49013">1777 1.2 ComputedStyle::GetStyleData(nsStyleStructID)</a>
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<a href="#21380">1600 1.1 __libc_malloc</a>
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<a href="#603">1552 1.0 nsCOMPtr_base::~nsCOMPtr_base()</a>
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</pre> </blockquote>
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This shows that of the 151603 times the timer fired, 1777 (1.2% of the total) were inside ComputedStyle::GetStyleData() and 1552 (1.0% of the total) were in the nsCOMPtr_base destructor.
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<p>
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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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<h4><a name="hier">Hierarchical output</a></h4>
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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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index Count Hits Function Name
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<A href="#72871"> 545 (46.4%) nsBlockFrame::ReflowInlineFrames(nsBlockReflowState&, nsLineList_iterator, int*)</A>
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<A href="#72873"> 100 (8.5%) nsBlockFrame::ReflowDirtyLines(nsBlockReflowState&)</A>
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72870 4 (0.3%) <a name=72870> 645 (54.9%)</a> <b>nsBlockFrame::DoReflowInlineFrames(nsBlockReflowState&, nsLineLayout&, nsLineList_iterator, nsFlowAreaRect&, int&, nsFloatManager::SavedState*, int*, LineReflowStatus*, int)</b>
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<A href="#72821"> 545 (46.4%) nsBlockFrame::ReflowInlineFrame(nsBlockReflowState&, nsLineLayout&, nsLineList_iterator, nsIFrame*, LineReflowStatus*)</A>
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<A href="#72853"> 83 (7.1%) nsBlockFrame::PlaceLine(nsBlockReflowState&, nsLineLayout&, nsLineList_iterator, nsFloatManager::SavedState*, nsRect&, int&, int*)</A>
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<A href="#74150"> 9 (0.8%) nsLineLayout::BeginLineReflow(int, int, int, int, int, int)</A>
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<A href="#74897"> 1 (0.1%) nsTextFrame::GetType() const</A>
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<A href="#74131"> 1 (0.1%) nsLineLayout::RelativePositionFrames(nsOverflowAreas&)</A>
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<A href="#58320"> 1 (0.1%) __i686.get_pc_thunk.bx</A>
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<A href="#53077"> 1 (0.1%) PL_ArenaAllocate</A>
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</pre></blockquote>
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The information this block tells us is:
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<ul>
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<li>There were 4 profiler hits <em>in</em> <code>nsBlockFrame::DoReflowInlineFrames</code>
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<li>There were 645 profiler hits <em>in or under</em> <code>nsBlockFrame::DoReflowInlineFrames</code>. Of these:
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<ul>
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<li>545 were in or under <code>nsBlockFrame::ReflowInlineFrame</code>
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<li>83 were in or under <code>nsBlockFrame::PlaceLine</code>
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<li>9 were in or under <code>nsLineLayout::BeginLineReflow</code>
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<li>1 was in or under <code>nsTextFrame::GetType</code>
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<li>1 was in or under <code>nsLineLayout::RelativePositionFrames</code>
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<li>1 was in or under <code>__i686.get_pc_thunk.bx</code>
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<li>1 was in or under <code>PL_ArenaAllocate</code>
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</ul>
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<li>Of these 645 calls into <code>nsBlockFrame::DoReflowInlineFrames</code>:
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<ul>
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<li>545 came from <code>nsBlockFrame::ReflowInlineFrames</code>
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<li>100 came from <code>nsBlockFrame::ReflowDirtyLines</code>
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</ul>
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</ul>
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The rest of this section explains how to read this information off from the jprof output.
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<p>This block corresponds to the function <code>nsBlockFrame::DoReflowInlineFrames</code>, which is
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therefore bolded and not a link. The name of this function is preceded by
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five numbers which have the following meaning. The number on the left (72870)
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is the index number, and is not important. The next number (4) and the
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percentage following (0.3%) are the number
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of times this function was interrupted by the timer and the percentage of
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the total hits that is. The last number pair ("645 (54.9%)")
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are the number of times this function was in the call stack when the timer went
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off. That is, the timer went off while we were in code that was ultimately
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called from <code>nsBlockFrame::DoReflowInlineFrames</code>.
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<p>For our example we can see that our function was in the call stack for
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645 interrupt ticks, but we were only the function that was running when
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the interrupt arrived 4 times.
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<P>
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The functions listed above the line for <code>nsBlockFrame::DoReflowInlineFrames</code> are its
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callers. The numbers to the left of these function names are the numbers of
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times these functions were in the call stack as callers of
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<code>nsBlockFrame::DoReflowInlineFrames</code>. In our example, we were called 545 times by
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<code>nsBlockFrame::ReflowInlineFrames</code> and 100 times by
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<code>nsBlockFrame::ReflowDirtyLines</code>.
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<P>
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The functions listed below the line for <code>nsBlockFrame::DoReflowInlineFrames</code> are its
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callees. The numbers to the left of the function names are the numbers of
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times these functions were in the callstack as callees of
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<code>nsBlockFrame::DoReflowInlineFrames</code> and the corresponding percentages. In our example, of the 645 profiler hits under <code>nsBlockFrame::DoReflowInlineFrames</code> 545 were under <code>nsBlockFrame::ReflowInlineFrame</code>, 83 were under <code>nsBlockFrame::PlaceLine</code>, and so forth.<p>
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<b>NOTE:</b> If there are loops of execution or recursion, the numbers will
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not add up and percentages can exceed 100%. If a function directly calls
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itself "(self)" will be appended to the line, but indirect recursion will
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not be marked.
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<h3>Bugs</h3>
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The current build of Jprof has only been tested under Ubuntu 8.04 LTS, but
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should work under any fairly modern linux distribution using GCC/GLIBC.
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Please update this document with any known compatibilities/incompatibilities.
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<p>
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If you get an error:<p><code>Inconsistency detected by ld.so: dl-open.c: 260: dl_open_worker: Assertion `_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT' failed!
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</code><p>that means you've hit a timing hole in the version of glibc you're
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running. See <a
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href="http://sources.redhat.com/bugzilla/show_bug.cgi?id=4578">Redhat bug 4578</a>.
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<!-- <h3>Update</h3>
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<ul>
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</ul>
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-->
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</body>
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</html>
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