1 <chapter id="profiling">
2 <title>Profiling</Title>
3 <indexterm><primary>profiling</primary>
5 <indexterm><primary>cost-centre profiling</primary></indexterm>
7 <para> Glasgow Haskell comes with a time and space profiling
8 system. Its purpose is to help you improve your understanding of
9 your program's execution behaviour, so you can improve it.</para>
11 <para> Any comments, suggestions and/or improvements you have are
12 welcome. Recommended “profiling tricks” would be
13 especially cool! </para>
15 <para>Profiling a program is a three-step process:</para>
19 <para> Re-compile your program for profiling with the
20 <literal>-prof</literal> option, and probably one of the
21 <literal>-auto</literal> or <literal>-auto-all</literal>
22 options. These options are described in more detail in <xref
23 linkend="prof-compiler-options"> </para>
24 <indexterm><primary><literal>-prof</literal></primary>
26 <indexterm><primary><literal>-auto</literal></primary>
28 <indexterm><primary><literal>-auto-all</literal></primary>
33 <para> Run your program with one of the profiling options, eg.
34 <literal>+RTS -p -RTS</literal>. This generates a file of
35 profiling information.</para>
36 <indexterm><primary><option>-p</option></primary><secondary>RTS
37 option</secondary></indexterm>
41 <para> Examine the generated profiling information, using one of
42 GHC's profiling tools. The tool to use will depend on the kind
43 of profiling information generated.</para>
49 <title>Cost centres and cost-centre stacks</title>
51 <para>GHC's profiling system assigns <firstterm>costs</firstterm>
52 to <firstterm>cost centres</firstterm>. A cost is simply the time
53 or space required to evaluate an expression. Cost centres are
54 program annotations around expressions; all costs incurred by the
55 annotated expression are assigned to the enclosing cost centre.
56 Furthermore, GHC will remember the stack of enclosing cost centres
57 for any given expression at run-time and generate a call-graph of
58 cost attributions.</para>
60 <para>Let's take a look at an example:</para>
63 main = print (nfib 25)
64 nfib n = if n < 2 then 1 else nfib (n-1) + nfib (n-2)
67 <para>Compile and run this program as follows:</para>
70 $ ghc -prof -auto-all -o Main Main.hs
76 <para>When a GHC-compiled program is run with the
77 <option>-p</option> RTS option, it generates a file called
78 <filename><prog>.prof</filename>. In this case, the file
79 will contain something like this:</para>
82 Fri May 12 14:06 2000 Time and Allocation Profiling Report (Final)
86 total time = 0.14 secs (7 ticks @ 20 ms)
87 total alloc = 8,741,204 bytes (excludes profiling overheads)
89 COST CENTRE MODULE %time %alloc
95 COST CENTRE MODULE entries %time %alloc %time %alloc
97 MAIN MAIN 0 0.0 0.0 100.0 100.0
98 main Main 0 0.0 0.0 0.0 0.0
99 CAF PrelHandle 3 0.0 0.0 0.0 0.0
100 CAF PrelAddr 1 0.0 0.0 0.0 0.0
101 CAF Main 6 0.0 0.0 100.0 100.0
102 main Main 1 0.0 0.0 100.0 100.0
103 nfib Main 242785 100.0 100.0 100.0 100.0
107 <para>The first part of the file gives the program name and
108 options, and the total time and total memory allocation measured
109 during the run of the program (note that the total memory
110 allocation figure isn't the same as the amount of
111 <emphasis>live</emphasis> memory needed by the program at any one
112 time; the latter can be determined using heap profiling, which we
113 will describe shortly).</para>
115 <para>The second part of the file is a break-down by cost centre
116 of the most costly functions in the program. In this case, there
117 was only one significant function in the program, namely
118 <function>nfib</function>, and it was responsible for 100%
119 of both the time and allocation costs of the program.</para>
121 <para>The third and final section of the file gives a profile
122 break-down by cost-centre stack. This is roughly a call-graph
123 profile of the program. In the example above, it is clear that
124 the costly call to <function>nfib</function> came from
125 <function>main</function>.</para>
127 <para>The time and allocation incurred by a given part of the
128 program is displayed in two ways: “individual”, which
129 are the costs incurred by the code covered by this cost centre
130 stack alone, and “inherited”, which includes the costs
131 incurred by all the children of this node.</para>
133 <para>The usefulness of cost-centre stacks is better demonstrated
134 by modifying the example slightly:</para>
137 main = print (f 25 + g 25)
139 g n = nfib (n `div` 2)
140 nfib n = if n < 2 then 1 else nfib (n-1) + nfib (n-2)
143 <para>Compile and run this program as before, and take a look at
144 the new profiling results:</para>
147 COST CENTRE MODULE scc %time %alloc %time %alloc
149 MAIN MAIN 0 0.0 0.0 100.0 100.0
150 main Main 0 0.0 0.0 0.0 0.0
151 CAF PrelHandle 3 0.0 0.0 0.0 0.0
152 CAF PrelAddr 1 0.0 0.0 0.0 0.0
153 CAF Main 9 0.0 0.0 100.0 100.0
154 main Main 1 0.0 0.0 100.0 100.0
155 g Main 1 0.0 0.0 0.0 0.2
156 nfib Main 465 0.0 0.2 0.0 0.2
157 f Main 1 0.0 0.0 100.0 99.8
158 nfib Main 242785 100.0 99.8 100.0 99.8
161 <para>Now although we had two calls to <function>nfib</function>
162 in the program, it is immediately clear that it was the call from
163 <function>f</function> which took all the time.</para>
165 <para>The actual meaning of the various columns in the output is:</para>
171 <para>The number of times this particular point in the call
172 graph was entered.</para>
177 <term>individual %time</term>
179 <para>The percentage of the total run time of the program
180 spent at this point in the call graph.</para>
185 <term>individual %alloc</term>
187 <para>The percentage of the total memory allocations
188 (excluding profiling overheads) of the program made by this
194 <term>inherited %time</term>
196 <para>The percentage of the total run time of the program
197 spent below this point in the call graph.</para>
202 <term>inherited %alloc</term>
204 <para>The percentage of the total memory allocations
205 (excluding profiling overheads) of the program made by this
206 call and all of its sub-calls.</para>
211 <para>In addition you can use the <Option>-P</Option> RTS option
212 <indexterm><primary><option>-P</option></primary></indexterm> to
213 get the following additional information:</para>
217 <term><literal>ticks</literal></term>
219 <para>The raw number of time “ticks” which were
220 attributed to this cost-centre; from this, we get the
221 <literal>%time</literal> figure mentioned
227 <term><literal>bytes</literal></term>
229 <para>Number of bytes allocated in the heap while in this
230 cost-centre; again, this is the raw number from which we get
231 the <literal>%alloc</literal> figure mentioned
237 <para>What about recursive functions, and mutually recursive
238 groups of functions? Where are the costs attributed? Well,
239 although GHC does keep information about which groups of functions
240 called each other recursively, this information isn't displayed in
241 the basic time and allocation profile, instead the call-graph is
242 flattened into a tree. The XML profiling tool (described in <xref
243 linkend="prof-xml-tool">) will be able to display real loops in
244 the call-graph.</para>
246 <sect2><title>Inserting cost centres by hand</title>
248 <para>Cost centres are just program annotations. When you say
249 <option>-auto-all</option> to the compiler, it automatically
250 inserts a cost centre annotation around every top-level function
251 in your program, but you are entirely free to add the cost
252 centre annotations yourself.</para>
254 <para>The syntax of a cost centre annotation is</para>
257 {-# SCC "name" #-} <expression>
260 <para>where <literal>"name"</literal> is an aribrary string,
261 that will become the name of your cost centre as it appears
262 in the profiling output, and
263 <literal><expression></literal> is any Haskell
264 expression. An <literal>SCC</literal> annotation extends as
265 far to the right as possible when parsing.</para>
269 <sect2 id="prof-rules">
270 <title>Rules for attributing costs</title>
272 <para>The cost of evaluating any expression in your program is
273 attributed to a cost-centre stack using the following rules:</para>
277 <para>If the expression is part of the
278 <firstterm>one-off</firstterm> costs of evaluating the
279 enclosing top-level definition, then costs are attributed to
280 the stack of lexically enclosing <literal>SCC</literal>
281 annotations on top of the special <literal>CAF</literal>
286 <para>Otherwise, costs are attributed to the stack of
287 lexically-enclosing <literal>SCC</literal> annotations,
288 appended to the cost-centre stack in effect at the
289 <firstterm>call site</firstterm> of the current top-level
290 definition<footnote> <para>The call-site is just the place
291 in the source code which mentions the particular function or
292 variable.</para></footnote>. Notice that this is a recursive
297 <para>Time spent in foreign code (see <xref linkend="ffi">)
298 is always attributed to the cost centre in force at the
299 Haskell call-site of the foreign function.</para>
303 <para>What do we mean by one-off costs? Well, Haskell is a lazy
304 language, and certain expressions are only ever evaluated once.
305 For example, if we write:</para>
311 <para>then <varname>x</varname> will only be evaluated once (if
312 at all), and subsequent demands for <varname>x</varname> will
313 immediately get to see the cached result. The definition
314 <varname>x</varname> is called a CAF (Constant Applicative
315 Form), because it has no arguments.</para>
317 <para>For the purposes of profiling, we say that the expression
318 <literal>nfib 25</literal> belongs to the one-off costs of
319 evaluating <varname>x</varname>.</para>
321 <para>Since one-off costs aren't strictly speaking part of the
322 call-graph of the program, they are attributed to a special
323 top-level cost centre, <literal>CAF</literal>. There may be one
324 <literal>CAF</literal> cost centre for each module (the
325 default), or one for each top-level definition with any one-off
326 costs (this behaviour can be selected by giving GHC the
327 <option>-caf-all</option> flag).</para>
329 <indexterm><primary><literal>-caf-all</literal></primary>
332 <para>If you think you have a weird profile, or the call-graph
333 doesn't look like you expect it to, feel free to send it (and
334 your program) to us at
335 <email>glasgow-haskell-bugs@haskell.org</email>.</para>
339 <sect1 id="prof-compiler-options">
340 <title>Compiler options for profiling</title>
342 <indexterm><primary>profiling</primary><secondary>options</secondary></indexterm>
343 <indexterm><primary>options</primary><secondary>for profiling</secondary></indexterm>
347 <term><Option>-prof</Option>:</Term>
348 <indexterm><primary><option>-prof</option></primary></indexterm>
350 <para> To make use of the profiling system
351 <emphasis>all</emphasis> modules must be compiled and linked
352 with the <option>-prof</option> option. Any
353 <literal>SCC</literal> annotations you've put in your source
354 will spring to life.</para>
356 <para> Without a <option>-prof</option> option, your
357 <literal>SCC</literal>s are ignored; so you can compile
358 <literal>SCC</literal>-laden code without changing
364 <para>There are a few other profiling-related compilation options.
365 Use them <emphasis>in addition to</emphasis>
366 <option>-prof</option>. These do not have to be used consistently
367 for all modules in a program.</para>
371 <term><option>-auto</option>:</Term>
372 <indexterm><primary><option>-auto</option></primary></indexterm>
373 <indexterm><primary>cost centres</primary><secondary>automatically inserting</secondary></indexterm>
375 <para> GHC will automatically add
376 <Function>_scc_</Function> constructs for all
377 top-level, exported functions.</para>
382 <term><option>-auto-all</option>:</Term>
383 <indexterm><primary><option>-auto-all</option></primary></indexterm>
385 <para> <Emphasis>All</Emphasis> top-level functions,
386 exported or not, will be automatically
387 <Function>_scc_</Function>'d.</para>
392 <term><option>-caf-all</option>:</Term>
393 <indexterm><primary><option>-caf-all</option></primary></indexterm>
395 <para> The costs of all CAFs in a module are usually
396 attributed to one “big” CAF cost-centre. With
397 this option, all CAFs get their own cost-centre. An
398 “if all else fails” option…</para>
403 <term><option>-ignore-scc</option>:</Term>
404 <indexterm><primary><option>-ignore-scc</option></primary></indexterm>
406 <para>Ignore any <Function>_scc_</Function>
407 constructs, so a module which already has
408 <Function>_scc_</Function>s can be compiled
409 for profiling with the annotations ignored.</para>
417 <sect1 id="prof-time-options">
418 <title>Time and allocation profiling</Title>
420 <para>To generate a time and allocation profile, give one of the
421 following RTS options to the compiled program when you run it (RTS
422 options should be enclosed between <literal>+RTS...-RTS</literal>
427 <term><Option>-p</Option> or <Option>-P</Option>:</Term>
428 <indexterm><primary><option>-p</option></primary></indexterm>
429 <indexterm><primary><option>-P</option></primary></indexterm>
430 <indexterm><primary>time profile</primary></indexterm>
432 <para>The <Option>-p</Option> option produces a standard
433 <Emphasis>time profile</Emphasis> report. It is written
435 <Filename><replaceable>program</replaceable>.prof</Filename>.</para>
437 <para>The <Option>-P</Option> option produces a more
438 detailed report containing the actual time and allocation
439 data as well. (Not used much.)</para>
444 <term><option>-px</option>:</term>
445 <indexterm><primary><option>-px</option></primary></indexterm>
447 <para>The <option>-px</option> option generates profiling
448 information in the XML format understood by our new
449 profiling tool, see <xref linkend="prof-xml-tool">.</para>
454 <term><option>-xc</option></term>
455 <indexterm><primary><option>-xc</option></primary><secondary>RTS
456 option</secondary></indexterm>
458 <para>This option makes use of the extra information
459 maintained by the cost-centre-stack profiler to provide
460 useful information about the location of runtime errors.
461 See <xref linkend="rts-options-debugging">.</para>
469 <sect1 id="prof-heap">
470 <title>Profiling memory usage</title>
472 <para>In addition to profiling the time and allocation behaviour
473 of your program, you can also generate a graph of its memory usage
474 over time. This is useful for detecting the causes of
475 <firstterm>space leaks</firstterm>, when your program holds on to
476 more memory at run-time that it needs to. Space leaks lead to
477 longer run-times due to heavy garbage collector ativity, and may
478 even cause the program to run out of memory altogether.</para>
480 <para>To generate a heap profile from your program:</para>
484 <para>Compile the program for profiling (<xref
485 linkend="prof-compiler-options">).</para>
488 <para>Run it with one of the heap profiling options described
489 below (eg. <option>-hc</option> for a basic producer profile).
490 This generates the file
491 <filename><replaceable>prog</replaceable>.hp</filename>.</para>
494 <para>Run <command>hp2ps</command> to produce a Postscript
496 <filename><replaceable>prog</replaceable>.ps</filename>. The
497 <command>hp2ps</command> utility is described in detail in
498 <xref linkend="hp2ps">.</para>
501 <para>Display the heap profile using a postscript viewer such
502 as <application>Ghostview</application>, or print it out on a
503 Postscript-capable printer.</para>
507 <sect2 id="rts-options-heap-prof">
508 <title>RTS options for heap profiling</title>
510 <para>There are several different kinds of heap profile that can
511 be generated. All the different profile types yield a graph of
512 live heap against time, but they differ in how the live heap is
513 broken down into bands. The following RTS options select which
514 break-down to use:</para>
518 <term><option>-hc</option></term>
519 <indexterm><primary><option>-hc</option></primary><secondary>RTS
520 option</secondary></indexterm>
522 <para>Breaks down the graph by the cost-centre stack which
523 produced the data.</para>
528 <term><option>-hm</option></term>
529 <indexterm><primary><option>-hm</option></primary><secondary>RTS
530 option</secondary></indexterm>
532 <para>Break down the live heap by the module containing
533 the code which produced the data.</para>
538 <term><option>-hd</option></term>
539 <indexterm><primary><option>-hd</option></primary><secondary>RTS
540 option</secondary></indexterm>
542 <para>Breaks down the graph by <firstterm>closure
543 description</firstterm>. For actual data, the description
544 is just the constructor name, for other closures it is a
545 compiler-generated string identifying the closure.</para>
550 <term><option>-hy</option></term>
551 <indexterm><primary><option>-hy</option></primary><secondary>RTS
552 option</secondary></indexterm>
554 <para>Breaks down the graph by
555 <firstterm>type</firstterm>. For closures which have
556 function type or unknown/polymorphic type, the string will
557 represent an approximation to the actual type.</para>
562 <term><option>-hr</option></term>
563 <indexterm><primary><option>-hr</option></primary><secondary>RTS
564 option</secondary></indexterm>
566 <para>Break down the graph by <firstterm>retainer
567 set</firstterm>. Retainer profiling is described in more
568 detail below (<xref linkend="retainer-prof">).</para>
573 <term><option>-hb</option></term>
574 <indexterm><primary><option>-hb</option></primary><secondary>RTS
575 option</secondary></indexterm>
577 <para>Break down the graph by
578 <firstterm>biography</firstterm>. Biographical profiling
579 is described in more detail below (<xref
580 linkend="biography-prof">).</para>
585 <para>In addition, the profile can be restricted to heap data
586 which satisfies certain criteria - for example, you might want
587 to display a profile by type but only for data produced by a
588 certain module, or a profile by retainer for a certain type of
589 data. Restrictions are specified as follows:</para>
593 <term><option>-hc</option><replaceable>name</replaceable>,...</term>
594 <indexterm><primary><option>-hc</option></primary><secondary>RTS
595 option</secondary></indexterm>
597 <para>Restrict the profile to closures produced by
598 cost-centre stacks with one of the specified cost centres
604 <term><option>-hC</option><replaceable>name</replaceable>,...</term>
605 <indexterm><primary><option>-hC</option></primary><secondary>RTS
606 option</secondary></indexterm>
608 <para>Restrict the profile to closures produced by
609 cost-centre stacks with one of the specified cost centres
610 anywhere in the stack.</para>
615 <term><option>-hm</option><replaceable>module</replaceable>,...</term>
616 <indexterm><primary><option>-hm</option></primary><secondary>RTS
617 option</secondary></indexterm>
619 <para>Restrict the profile to closures produced by the
620 specified modules.</para>
625 <term><option>-hd</option><replaceable>desc</replaceable>,...</term>
626 <indexterm><primary><option>-hd</option></primary><secondary>RTS
627 option</secondary></indexterm>
629 <para>Restrict the profile to closures with the specified
630 description strings.</para>
635 <term><option>-hy</option><replaceable>type</replaceable>,...</term>
636 <indexterm><primary><option>-hy</option></primary><secondary>RTS
637 option</secondary></indexterm>
639 <para>Restrict the profile to closures with the specified
645 <term><option>-hr</option><replaceable>cc</replaceable>,...</term>
646 <indexterm><primary><option>-hr</option></primary><secondary>RTS
647 option</secondary></indexterm>
649 <para>Restrict the profile to closures with retainer sets
650 containing cost-centre stacks with one of the specified
651 cost centres at the top.</para>
656 <term><option>-hb</option><replaceable>bio</replaceable>,...</term>
657 <indexterm><primary><option>-hb</option></primary><secondary>RTS
658 option</secondary></indexterm>
660 <para>Restrict the profile to closures with one of the
661 specified biographies, where
662 <replaceable>bio</replaceable> is one of
663 <literal>lag</literal>, <literal>drag</literal>,
664 <literal>void</literal>, or <literal>use</literal>.</para>
669 <para>For example, the following options will generate a
670 retainer profile restricted to <literal>Branch</literal> and
671 <literal>Leaf</literal> constructors:</para>
674 <replaceable>prog</replaceable> +RTS -hr -hdBranch,Leaf
677 <para>There can only be one "break-down" option
678 (eg. <option>-hr</option> in the example above), but there is no
679 limit on the number of further restrictions that may be applied.
680 All the options may be combined, with one exception: GHC doesn't
681 currently support mixing the <option>-hr</option> and
682 <option>-hb</option> options.</para>
684 <para>There's one more option which relates to heap
689 <term><Option>-i<replaceable>secs</replaceable></Option>:</Term>
690 <indexterm><primary><option>-i</option></primary></indexterm>
692 <para> Set the profiling (sampling) interval to
693 <replaceable>secs</replaceable> seconds (the default is
694 0.1 second). Fractions are allowed: for example
695 <Option>-i0.2</Option> will get 5 samples per second.
696 This only affects heap profiling; time profiles are always
697 sampled on a 1/50 second frequency.</para>
704 <sect2 id="retainer-prof">
705 <title>Retainer Profiling</title>
707 <para>Retainer profiling is designed to help answer questions
708 like <quote>why is this data being retained?</quote>. We start
709 by defining what we mean by a retainer:</para>
712 <para>A retainer is either the system stack, or an unevaluated
713 closure (thunk).</para>
716 <para>In particular, constructors are <emphasis>not</emphasis>
719 <para>An object A is retained by an object B if object A can be
720 reached by recursively following pointers starting from object
721 B but not meeting any other retainers on the way. Each object
722 has one or more retainers, collectively called its
723 <firstterm>retainer set</firstterm>.</para>
725 <para>When retainer profiling is requested by giving the program
726 the <option>-hr</option> option, a graph is generated which is
727 broken down by retainer set. A retainer set is displayed as a
728 set of cost-centre stacks; because this is usually too large to
729 fit on the profile graph, each retainer set is numbered and
730 shown abbreviated on the graph along with its number, and the
731 full list of retainer sets is dumped into the file
732 <filename><replaceable>prog</replaceable>.prof</filename>.</para>
734 <para>Retainer profiling requires multiple passes over the live
735 heap in order to discover the full retainer set for each
736 object, which can be quite slow. So we set a limit on the
737 maximum size of a retainer set, where all retainer sets larger
738 than the maximum retainer set size are replaced by the special
739 set <literal>MANY</literal>. The maximum set size defaults to 8
740 and can be altered with the <option>-R</option> RTS
745 <term><option>-R</option><replaceable>size</replaceable></term>
747 <para>Restrict the number of elements in a retainer set to
748 <replaceable>size</replaceable> (default 8).</para>
754 <title>Hints for using retainer profiling</title>
756 <para>The definition of retainers is designed to reflect a
757 common cause of space leaks: a large structure is retained by
758 an unevaluated computation, and will be released once the
759 compuation is forced. A good example is looking up a value in
760 a finite map, where unless the lookup is forced in a timely
761 manner the unevaluated lookup will cause the whole mapping to
762 be retained. These kind of space leaks can often be
763 eliminated by forcing the relevant computations to be
764 performed eagerly, using <literal>seq</literal> or strictness
765 annotations on data constructor fields.</para>
767 <para>Often a particular data structure is being retained by a
768 chain of unevaluated closures, only the nearest of which will
769 be reported by retainer profiling - for example A retains B, B
770 retains C, and C retains a large structure. There might be a
771 large number of Bs but only a single A, so A is really the one
772 we're interested in eliminating. However, retainer profiling
773 will in this case report B as the retainer of the large
774 structure. To move further up the chain of retainers, we can
775 ask for another retainer profile but this time restrict the
776 profile to B objects, so we get a profile of the retainers of
780 <replaceable>prog</replaceable> +RTS -hr -hcB
783 <para>This trick isn't foolproof, because there might be other
784 B closures in the heap which aren't the retainers we are
785 interested in, but we've found this to be a useful technique
786 in most cases.</para>
790 <sect2 id="biography-prof">
791 <title>Biographical Profiling</title>
793 <para>A typical heap object may be in one of the following four
794 states at each point in its lifetime:</para>
798 <para>The <firstterm>lag</firstterm> stage, which is the
799 time between creation and the first use of the
803 <para>the <firstterm>use</firstterm> stage, which lasts from
804 the first use until the last use of the object, and</para>
807 <para>The <firstterm>drag</firstterm> stage, which lasts
808 from the final use until the last reference to the object
812 <para>An object which is never used is said to be in the
813 <firstterm>void</firstterm> state for its whole
818 <para>A biographical heap profile displays the portion of the
819 live heap in each of the four states listed above. Usually the
820 most interesting states are the void and drag states: live heap
821 in these states is more likely to be wasted space than heap in
822 the lag or use states.</para>
824 <para>It is also possible to break down the heap in one or more
825 of these states by a different criteria, by restricting a
826 profile by biography. For example, to show the portion of the
827 heap in the drag or void state by producer: </para>
830 <replaceable>prog</replaceable> +RTS -hc -hbdrag,void
833 <para>Once you know the producer or the type of the heap in the
834 drag or void states, the next step is usually to find the
838 <replaceable>prog</replaceable> +RTS -hr -hc<replaceable>cc</replaceable>...
841 <para>NOTE: this two stage process is required because GHC
842 cannot currently profile using both biographical and retainer
843 information simultaneously.</para>
848 <sect1 id="prof-xml-tool">
849 <title>Graphical time/allocation profile</title>
851 <para>You can view the time and allocation profiling graph of your
852 program graphically, using <command>ghcprof</command>. This is a
853 new tool with GHC 4.08, and will eventually be the de-facto
854 standard way of viewing GHC profiles<footnote><para>Actually this
855 isn't true any more, we are working on a new tool for
856 displaying heap profiles using Gtk+HS, so
857 <command>ghcprof</command> may go away at some point in the future.</para>
860 <para>To run <command>ghcprof</command>, you need
861 <productname>daVinci</productname> installed, which can be
863 url="http://www.informatik.uni-bremen.de/daVinci/"><citetitle>The Graph
864 Visualisation Tool daVinci</citetitle></ulink>. Install one of
866 distributions<footnote><para><productname>daVinci</productname> is
867 sadly not open-source :-(.</para></footnote>, and set your
868 <envar>DAVINCIHOME</envar> environment variable to point to the
869 installation directory.</para>
871 <para><command>ghcprof</command> uses an XML-based profiling log
872 format, and you therefore need to run your program with a
873 different option: <option>-px</option>. The file generated is
874 still called <filename><prog>.prof</filename>. To see the
875 profile, run <command>ghcprof</command> like this:</para>
877 <indexterm><primary><option>-px</option></primary></indexterm>
880 $ ghcprof <prog>.prof
883 <para>which should pop up a window showing the call-graph of your
884 program in glorious detail. More information on using
885 <command>ghcprof</command> can be found at <ulink
886 url="http://www.dcs.warwick.ac.uk/people/academic/Stephen.Jarvis/profiler/index.html"><citetitle>The
887 Cost-Centre Stack Profiling Tool for
888 GHC</citetitle></ulink>.</para>
893 <title><command>hp2ps</command>––heap profile to PostScript</title>
895 <indexterm><primary><command>hp2ps</command></primary></indexterm>
896 <indexterm><primary>heap profiles</primary></indexterm>
897 <indexterm><primary>postscript, from heap profiles</primary></indexterm>
898 <indexterm><primary><option>-h<break-down></option></primary></indexterm>
903 hp2ps [flags] [<file>[.hp]]
907 <command>hp2ps</command><indexterm><primary>hp2ps
908 program</primary></indexterm> converts a heap profile as produced
909 by the <Option>-h<break-down></Option> runtime option into a
910 PostScript graph of the heap profile. By convention, the file to
911 be processed by <command>hp2ps</command> has a
912 <filename>.hp</filename> extension. The PostScript output is
913 written to <filename><file>@.ps</filename>. If
914 <filename><file></filename> is omitted entirely, then the
915 program behaves as a filter.</para>
917 <para><command>hp2ps</command> is distributed in
918 <filename>ghc/utils/hp2ps</filename> in a GHC source
919 distribution. It was originally developed by Dave Wakeling as part
920 of the HBC/LML heap profiler.</para>
922 <para>The flags are:</para>
927 <term><Option>-d</Option></Term>
929 <para>In order to make graphs more readable,
930 <command>hp2ps</command> sorts the shaded bands for each
931 identifier. The default sort ordering is for the bands with
932 the largest area to be stacked on top of the smaller ones.
933 The <Option>-d</Option> option causes rougher bands (those
934 representing series of values with the largest standard
935 deviations) to be stacked on top of smoother ones.</para>
940 <term><Option>-b</Option></Term>
942 <para>Normally, <command>hp2ps</command> puts the title of
943 the graph in a small box at the top of the page. However, if
944 the JOB string is too long to fit in a small box (more than
945 35 characters), then <command>hp2ps</command> will choose to
946 use a big box instead. The <Option>-b</Option> option
947 forces <command>hp2ps</command> to use a big box.</para>
952 <term><Option>-e<float>[in|mm|pt]</Option></Term>
954 <para>Generate encapsulated PostScript suitable for
955 inclusion in LaTeX documents. Usually, the PostScript graph
956 is drawn in landscape mode in an area 9 inches wide by 6
957 inches high, and <command>hp2ps</command> arranges for this
958 area to be approximately centred on a sheet of a4 paper.
959 This format is convenient of studying the graph in detail,
960 but it is unsuitable for inclusion in LaTeX documents. The
961 <Option>-e</Option> option causes the graph to be drawn in
962 portrait mode, with float specifying the width in inches,
963 millimetres or points (the default). The resulting
964 PostScript file conforms to the Encapsulated PostScript
965 (EPS) convention, and it can be included in a LaTeX document
966 using Rokicki's dvi-to-PostScript converter
967 <command>dvips</command>.</para>
972 <term><Option>-g</Option></Term>
974 <para>Create output suitable for the <command>gs</command>
975 PostScript previewer (or similar). In this case the graph is
976 printed in portrait mode without scaling. The output is
977 unsuitable for a laser printer.</para>
982 <term><Option>-l</Option></Term>
984 <para>Normally a profile is limited to 20 bands with
985 additional identifiers being grouped into an
986 <literal>OTHER</literal> band. The <Option>-l</Option> flag
987 removes this 20 band and limit, producing as many bands as
988 necessary. No key is produced as it won't fit!. It is useful
989 for creation time profiles with many bands.</para>
994 <term><Option>-m<int></Option></Term>
996 <para>Normally a profile is limited to 20 bands with
997 additional identifiers being grouped into an
998 <literal>OTHER</literal> band. The <Option>-m</Option> flag
999 specifies an alternative band limit (the maximum is
1002 <para><Option>-m0</Option> requests the band limit to be
1003 removed. As many bands as necessary are produced. However no
1004 key is produced as it won't fit! It is useful for displaying
1005 creation time profiles with many bands.</para>
1010 <term><Option>-p</Option></Term>
1012 <para>Use previous parameters. By default, the PostScript
1013 graph is automatically scaled both horizontally and
1014 vertically so that it fills the page. However, when
1015 preparing a series of graphs for use in a presentation, it
1016 is often useful to draw a new graph using the same scale,
1017 shading and ordering as a previous one. The
1018 <Option>-p</Option> flag causes the graph to be drawn using
1019 the parameters determined by a previous run of
1020 <command>hp2ps</command> on <filename>file</filename>. These
1021 are extracted from <filename>file@.aux</filename>.</para>
1026 <term><Option>-s</Option></Term>
1028 <para>Use a small box for the title.</para>
1033 <term><Option>-t<float></Option></Term>
1035 <para>Normally trace elements which sum to a total of less
1036 than 1% of the profile are removed from the
1037 profile. The <option>-t</option> option allows this
1038 percentage to be modified (maximum 5%).</para>
1040 <para><Option>-t0</Option> requests no trace elements to be
1041 removed from the profile, ensuring that all the data will be
1047 <term><Option>-c</Option></Term>
1049 <para>Generate colour output.</para>
1054 <term><Option>-y</Option></Term>
1056 <para>Ignore marks.</para>
1061 <term><Option>-?</Option></Term>
1063 <para>Print out usage information.</para>
1069 <sect1 id="ticky-ticky">
1070 <title>Using “ticky-ticky” profiling (for implementors)</Title>
1071 <indexterm><primary>ticky-ticky profiling</primary></indexterm>
1073 <para>(ToDo: document properly.)</para>
1075 <para>It is possible to compile Glasgow Haskell programs so that
1076 they will count lots and lots of interesting things, e.g., number
1077 of updates, number of data constructors entered, etc., etc. We
1078 call this “ticky-ticky”
1079 profiling,<indexterm><primary>ticky-ticky
1080 profiling</primary></indexterm> <indexterm><primary>profiling,
1081 ticky-ticky</primary></indexterm> because that's the sound a Sun4
1082 makes when it is running up all those counters
1083 (<Emphasis>slowly</Emphasis>).</para>
1085 <para>Ticky-ticky profiling is mainly intended for implementors;
1086 it is quite separate from the main “cost-centre”
1087 profiling system, intended for all users everywhere.</para>
1089 <para>To be able to use ticky-ticky profiling, you will need to
1090 have built appropriate libraries and things when you made the
1091 system. See “Customising what libraries to build,” in
1092 the installation guide.</para>
1094 <para>To get your compiled program to spit out the ticky-ticky
1095 numbers, use a <Option>-r</Option> RTS
1096 option<indexterm><primary>-r RTS option</primary></indexterm>.
1097 See <XRef LinkEnd="runtime-control">.</para>
1099 <para>Compiling your program with the <Option>-ticky</Option>
1100 switch yields an executable that performs these counts. Here is a
1101 sample ticky-ticky statistics file, generated by the invocation
1102 <command>foo +RTS -rfoo.ticky</command>.</para>
1105 foo +RTS -rfoo.ticky
1108 ALLOCATIONS: 3964631 (11330900 words total: 3999476 admin, 6098829 goods, 1232595 slop)
1109 total words: 2 3 4 5 6+
1110 69647 ( 1.8%) function values 50.0 50.0 0.0 0.0 0.0
1111 2382937 ( 60.1%) thunks 0.0 83.9 16.1 0.0 0.0
1112 1477218 ( 37.3%) data values 66.8 33.2 0.0 0.0 0.0
1113 0 ( 0.0%) big tuples
1114 2 ( 0.0%) black holes 0.0 100.0 0.0 0.0 0.0
1115 0 ( 0.0%) prim things
1116 34825 ( 0.9%) partial applications 0.0 0.0 0.0 100.0 0.0
1117 2 ( 0.0%) thread state objects 0.0 0.0 0.0 0.0 100.0
1119 Total storage-manager allocations: 3647137 (11882004 words)
1120 [551104 words lost to speculative heap-checks]
1124 ENTERS: 9400092 of which 2005772 (21.3%) direct to the entry code
1125 [the rest indirected via Node's info ptr]
1126 1860318 ( 19.8%) thunks
1127 3733184 ( 39.7%) data values
1128 3149544 ( 33.5%) function values
1129 [of which 1999880 (63.5%) bypassed arg-satisfaction chk]
1130 348140 ( 3.7%) partial applications
1131 308906 ( 3.3%) normal indirections
1132 0 ( 0.0%) permanent indirections
1135 2137257 ( 36.4%) from entering a new constructor
1136 [the rest from entering an existing constructor]
1137 2349219 ( 40.0%) vectored [the rest unvectored]
1139 RET_NEW: 2137257: 32.5% 46.2% 21.3% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
1140 RET_OLD: 3733184: 2.8% 67.9% 29.3% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
1141 RET_UNBOXED_TUP: 2: 0.0% 0.0%100.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
1143 RET_VEC_RETURN : 2349219: 0.0% 0.0%100.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0%
1145 UPDATE FRAMES: 2241725 (0 omitted from thunks)
1149 0 ( 0.0%) data values
1150 34827 ( 1.6%) partial applications
1151 [2 in place, 34825 allocated new space]
1152 2206898 ( 98.4%) updates to existing heap objects (46 by squeezing)
1153 UPD_CON_IN_NEW: 0: 0 0 0 0 0 0 0 0 0
1154 UPD_PAP_IN_NEW: 34825: 0 0 0 34825 0 0 0 0 0
1156 NEW GEN UPDATES: 2274700 ( 99.9%)
1158 OLD GEN UPDATES: 1852 ( 0.1%)
1160 Total bytes copied during GC: 190096
1162 **************************************************
1163 3647137 ALLOC_HEAP_ctr
1164 11882004 ALLOC_HEAP_tot
1169 34831 ALLOC_FUN_hst_0
1170 34816 ALLOC_FUN_hst_1
1174 2382937 ALLOC_UP_THK_ctr
1177 0 E!NT_PERM_IND_ctr requires +RTS -Z
1178 [... lots more info omitted ...]
1179 0 GC_SEL_ABANDONED_ctr
1182 0 GC_FAILED_PROMOTION_ctr
1183 47524 GC_WORDS_COPIED_ctr
1186 <para>The formatting of the information above the row of asterisks
1187 is subject to change, but hopefully provides a useful
1188 human-readable summary. Below the asterisks <Emphasis>all
1189 counters</Emphasis> maintained by the ticky-ticky system are
1190 dumped, in a format intended to be machine-readable: zero or more
1191 spaces, an integer, a space, the counter name, and a newline.</para>
1193 <para>In fact, not <Emphasis>all</Emphasis> counters are
1194 necessarily dumped; compile- or run-time flags can render certain
1195 counters invalid. In this case, either the counter will simply
1196 not appear, or it will appear with a modified counter name,
1197 possibly along with an explanation for the omission (notice
1198 <literal>ENT_PERM_IND_ctr</literal> appears
1199 with an inserted <literal>!</literal> above). Software analysing
1200 this output should always check that it has the counters it
1201 expects. Also, beware: some of the counters can have
1202 <Emphasis>large</Emphasis> values!</para>
1209 ;;; Local Variables: ***
1211 ;;; sgml-parent-document: ("users_guide.sgml" "book" "chapter") ***