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64 LuaJIT has an integrated statistical profiler with very low overhead. It
65 allows sampling the currently executing stack and other parameters in
69 The integrated profiler can be accessed from three levels:
72 <li>The
<a href=
"#hl_profiler">bundled high-level profiler
</a>, invoked by the
73 <a href=
"#j_p"><tt>-jp
</tt></a> command line option.
</li>
74 <li>A
<a href=
"#ll_lua_api">low-level Lua API
</a> to control the profiler.
</li>
75 <li>A
<a href=
"#ll_c_api">low-level C API
</a> to control the profiler.
</li>
78 <h2 id=
"hl_profiler">High-Level Profiler
</h2>
80 The bundled high-level profiler offers basic profiling functionality. It
81 generates simple textual summaries or source code annotations. It can be
82 accessed with the
<a href=
"#j_p"><tt>-jp
</tt></a> command line option
83 or from Lua code by loading the underlying
<tt>jit.p
</tt> module.
86 To cut to the chase
— run this to get a CPU usage profile by
93 It's
<em>not
</em> a stated goal of the bundled profiler to add every
94 possible option or to cater for special profiling needs. The low-level
95 profiler APIs are documented below. They may be used by third-party
96 authors to implement advanced functionality, e.g. IDE integration or
100 Note: Sampling works for both interpreted and JIT-compiled code. The
101 results for JIT-compiled code may sometimes be surprising. LuaJIT
102 heavily optimizes and inlines Lua code
— there's no simple
103 one-to-one correspondence between source code lines and the sampled
107 <h3 id=
"j_p"><tt>-jp=[options[,output]]
</tt></h3>
109 The
<tt>-jp
</tt> command line option starts the high-level profiler.
110 When the application run by the command line terminates, the profiler
111 stops and writes the results to
<tt>stdout
</tt> or to the specified
112 <tt>output
</tt> file.
115 The
<tt>options
</tt> argument specifies how the profiling is to be
119 <li><tt>f
</tt> — Stack dump: function name, otherwise module:line.
120 This is the default mode.
</li>
121 <li><tt>F
</tt> — Stack dump: ditto, but dump module:name.
</li>
122 <li><tt>l
</tt> — Stack dump: module:line.
</li>
123 <li><tt><number
></tt> — stack dump depth (callee
←
124 caller). Default:
1.
</li>
125 <li><tt>-
<number
></tt> — Inverse stack dump depth (caller
127 <li><tt>s
</tt> — Split stack dump after first stack level. Implies
128 depth
≥ 2 or depth
≤ -
2.
</li>
129 <li><tt>p
</tt> — Show full path for module names.
</li>
130 <li><tt>v
</tt> — Show VM states.
</li>
131 <li><tt>z
</tt> — Show
<a href=
"#jit_zone">zones
</a>.
</li>
132 <li><tt>r
</tt> — Show raw sample counts. Default: show percentages.
</li>
133 <li><tt>a
</tt> — Annotate excerpts from source code files.
</li>
134 <li><tt>A
</tt> — Annotate complete source code files.
</li>
135 <li><tt>G
</tt> — Produce raw output suitable for graphical tools.
</li>
136 <li><tt>m
<number
></tt> — Minimum sample percentage to be shown.
138 <li><tt>i
<number
></tt> — Sampling interval in milliseconds.
140 Note: The actual sampling precision is OS-dependent.
</li>
143 The default output for
<tt>-jp
</tt> is a list of the most CPU consuming
144 spots in the application. Increasing the stack dump depth with (say)
145 <tt>-jp=
2</tt> may help to point out the main callers or callees of
146 hotspots. But sample aggregation is still flat per unique stack dump.
149 To get a two-level view (split view) of callers/callees, use
150 <tt>-jp=s
</tt> or
<tt>-jp=-s
</tt>. The percentages shown for the second
151 level are relative to the first level.
154 To see how much time is spent in each line relative to a function, use
158 To see how much time is spent in different VM states or
159 <a href=
"#jit_zone">zones
</a>, use
<tt>-jp=v
</tt> or
<tt>-jp=z
</tt>.
162 Combinations of
<tt>v/z
</tt> with
<tt>f/F/l
</tt> produce two-level
163 views, e.g.
<tt>-jp=vf
</tt> or
<tt>-jp=fv
</tt>. This shows the time
164 spent in a VM state or zone vs. hotspots. This can be used to answer
165 questions like
"Which time consuming functions are only interpreted?" or
166 "What's the garbage collector overhead for a specific function?".
169 Multiple options can be combined
— but not all combinations make
170 sense, see above. E.g.
<tt>-jp=
3si4m1
</tt> samples three stack levels
171 deep in
4ms intervals and shows a split view of the CPU consuming
172 functions and their callers with a
1% threshold.
175 Source code annotations produced by
<tt>-jp=a
</tt> or
<tt>-jp=A
</tt> are
176 always flat and at the line level. Obviously, the source code files need
177 to be readable by the profiler script.
180 The high-level profiler can also be started and stopped from Lua code with:
183 require(
"jit.p").start(options, output)
185 require(
"jit.p").stop()
188 <h3 id=
"jit_zone"><tt>jit.zone
</tt> — Zones
</h3>
190 Zones can be used to provide information about different parts of an
191 application to the high-level profiler. E.g. a game could make use of an
192 <tt>"AI"</tt> zone, a
<tt>"PHYS"</tt> zone, etc. Zones are hierarchical,
193 organized as a stack.
196 The
<tt>jit.zone
</tt> module needs to be loaded explicitly:
199 local zone = require(
"jit.zone")
202 <li><tt>zone(
"name")
</tt> pushes a named zone to the zone stack.
</li>
203 <li><tt>zone()
</tt> pops the current zone from the zone stack and
204 returns its name.
</li>
205 <li><tt>zone:get()
</tt> returns the current zone name or
<tt>nil
</tt>.
</li>
206 <li><tt>zone:flush()
</tt> flushes the zone stack.
</li>
209 To show the time spent in each zone use
<tt>-jp=z
</tt>. To show the time
210 spent relative to hotspots use e.g.
<tt>-jp=zf
</tt> or
<tt>-jp=fz
</tt>.
213 <h2 id=
"ll_lua_api">Low-level Lua API
</h2>
215 The
<tt>jit.profile
</tt> module gives access to the low-level API of the
216 profiler from Lua code. This module needs to be loaded explicitly:
218 local profile = require(
"jit.profile")
221 This module can be used to implement your own higher-level profiler.
222 A typical profiling run starts the profiler, captures stack dumps in
223 the profiler callback, adds them to a hash table to aggregate the number
224 of samples, stops the profiler and then analyzes all of the captured
225 stack dumps. Other parameters can be sampled in the profiler callback,
226 too. But it's important not to spend too much time in the callback,
227 since this may skew the statistics.
230 <h3 id=
"profile_start"><tt>profile.start(mode, cb)
</tt>
231 — Start profiler
</h3>
233 This function starts the profiler. The
<tt>mode
</tt> argument is a
234 string holding options:
237 <li><tt>f
</tt> — Profile with precision down to the function level.
</li>
238 <li><tt>l
</tt> — Profile with precision down to the line level.
</li>
239 <li><tt>i
<number
></tt> — Sampling interval in milliseconds (default
241 Note: The actual sampling precision is OS-dependent.
245 The
<tt>cb
</tt> argument is a callback function which is called with
246 three arguments:
<tt>(thread, samples, vmstate)
</tt>. The callback is
247 called on a separate coroutine, the
<tt>thread
</tt> argument is the
248 state that holds the stack to sample for profiling. Note: do
249 <em>not
</em> modify the stack of that state or call functions on it.
252 <tt>samples
</tt> gives the number of accumulated samples since the last
253 callback (usually
1).
256 <tt>vmstate
</tt> holds the VM state at the time the profiling timer
257 triggered. This may or may not correspond to the state of the VM when
258 the profiling callback is called. The state is either
<tt>'N'
</tt>
259 native (compiled) code,
<tt>'I'
</tt> interpreted code,
<tt>'C'
</tt>
260 C
code,
<tt>'G'
</tt> the garbage collector, or
<tt>'J'
</tt> the JIT
264 <h3 id=
"profile_stop"><tt>profile.stop()
</tt>
265 — Stop profiler
</h3>
267 This function stops the profiler.
270 <h3 id=
"profile_dump"><tt>dump = profile.dumpstack([thread,] fmt, depth)
</tt>
271 — Dump stack
</h3>
273 This function allows taking stack dumps in an efficient manner. It
274 returns a string with a stack dump for the
<tt>thread
</tt> (coroutine),
275 formatted according to the
<tt>fmt
</tt> argument:
278 <li><tt>p
</tt> — Preserve the full path for module names. Otherwise
279 only the file name is used.
</li>
280 <li><tt>f
</tt> — Dump the function name if it can be derived. Otherwise
281 use module:line.
</li>
282 <li><tt>F
</tt> — Ditto, but dump module:name.
</li>
283 <li><tt>l
</tt> — Dump module:line.
</li>
284 <li><tt>Z
</tt> — Zap the following characters for the last dumped
286 <li>All other characters are added verbatim to the output string.
</li>
289 The
<tt>depth
</tt> argument gives the number of frames to dump, starting
290 at the topmost frame of the thread. A negative number dumps the frames in
294 The first example prints a list of the current module names and line
295 numbers of up to
10 frames in separate lines. The second example prints
296 semicolon-separated function names for all frames (up to
100) in inverse
300 print(profile.dumpstack(thread,
"l\n",
10))
301 print(profile.dumpstack(thread,
"lZ;", -
100))
304 <h2 id=
"ll_c_api">Low-level C API
</h2>
306 The profiler can be controlled directly from C
code, e.g. for
307 use by IDEs. The declarations are in
<tt>"luajit.h"</tt> (see
308 <a href=
"ext_c_api.html">Lua/C API
</a> extensions).
311 <h3 id=
"luaJIT_profile_start"><tt>luaJIT_profile_start(L, mode, cb, data)
</tt>
312 — Start profiler
</h3>
314 This function starts the profiler.
<a href=
"#profile_start">See
315 above
</a> for a description of the
<tt>mode
</tt> argument.
318 The
<tt>cb
</tt> argument is a callback function with the following
322 typedef void (*luaJIT_profile_callback)(void *data, lua_State *L,
323 int samples, int vmstate);
326 <tt>data
</tt> is available for use by the callback.
<tt>L
</tt> is the
327 state that holds the stack to sample for profiling. Note: do
328 <em>not
</em> modify this stack or call functions on this stack
—
329 use a separate coroutine for this purpose.
<a href=
"#profile_start">See
330 above
</a> for a description of
<tt>samples
</tt> and
<tt>vmstate
</tt>.
333 <h3 id=
"luaJIT_profile_stop"><tt>luaJIT_profile_stop(L)
</tt>
334 — Stop profiler
</h3>
336 This function stops the profiler.
339 <h3 id=
"luaJIT_profile_dumpstack"><tt>p = luaJIT_profile_dumpstack(L, fmt, depth, len)
</tt>
340 — Dump stack
</h3>
342 This function allows taking stack dumps in an efficient manner.
343 <a href=
"#profile_dump">See above
</a> for a description of
<tt>fmt
</tt>
347 This function returns a
<tt>const
char
*
</tt> pointing to a
348 private string buffer of the profiler. The
<tt>int
*len
</tt>
349 argument returns the length of the output string. The buffer is
350 overwritten on the next call and deallocated when the profiler stops.
351 You either need to consume the content immediately or copy it for later
358 Copyright
© 2005-
2015 Mike Pall
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