(ToDo: document properly.)
It is possible to compile Haskell programs so that they will count lots and lots of interesting things, e.g., number of updates, number of data constructors entered, etc., etc. We call this “ticky-ticky” profiling, because that's the sound a CPU makes when it is running up all those counters (slowly).
Ticky-ticky profiling is mainly intended for implementors; it is quite separate from the main “cost-centre” profiling system, intended for all users everywhere.
You don't need to build GHC, the libraries, or the RTS a special
way in order to use ticky-ticky profiling. You can decide on a
module-by-module basis which parts of a program have the
counters compiled in, using the
compile-time -ticky
option. Those modules that
were not compiled with -ticky
won't contribute
to the ticky-ticky profiling results, and that will normally
include all the pre-compiled packages that your program links
with.
To get your compiled program to spit out the ticky-ticky numbers:
Link the program with -debug
(-ticky
is a synonym
for -debug
at link-time). This links in
the debug version of the RTS, which includes the code for
aggregating and reporting the results of ticky-ticky
profilng.
Run the program with the -r
RTS
option.
See Section 4.16, “Running a compiled program”.
Here is a sample ticky-ticky statistics file, generated by the invocation foo +RTS -rfoo.ticky.
foo +RTS -rfoo.ticky ALLOCATIONS: 3964631 (11330900 words total: 3999476 admin, 6098829 goods, 1232595 slop) total words: 2 3 4 5 6+ 69647 ( 1.8%) function values 50.0 50.0 0.0 0.0 0.0 2382937 ( 60.1%) thunks 0.0 83.9 16.1 0.0 0.0 1477218 ( 37.3%) data values 66.8 33.2 0.0 0.0 0.0 0 ( 0.0%) big tuples 2 ( 0.0%) black holes 0.0 100.0 0.0 0.0 0.0 0 ( 0.0%) prim things 34825 ( 0.9%) partial applications 0.0 0.0 0.0 100.0 0.0 2 ( 0.0%) thread state objects 0.0 0.0 0.0 0.0 100.0 Total storage-manager allocations: 3647137 (11882004 words) [551104 words lost to speculative heap-checks] STACK USAGE: ENTERS: 9400092 of which 2005772 (21.3%) direct to the entry code [the rest indirected via Node's info ptr] 1860318 ( 19.8%) thunks 3733184 ( 39.7%) data values 3149544 ( 33.5%) function values [of which 1999880 (63.5%) bypassed arg-satisfaction chk] 348140 ( 3.7%) partial applications 308906 ( 3.3%) normal indirections 0 ( 0.0%) permanent indirections RETURNS: 5870443 2137257 ( 36.4%) from entering a new constructor [the rest from entering an existing constructor] 2349219 ( 40.0%) vectored [the rest unvectored] RET_NEW: 2137257: 32.5% 46.2% 21.3% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% RET_OLD: 3733184: 2.8% 67.9% 29.3% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% RET_UNBOXED_TUP: 2: 0.0% 0.0%100.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% RET_VEC_RETURN : 2349219: 0.0% 0.0%100.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% UPDATE FRAMES: 2241725 (0 omitted from thunks) SEQ FRAMES: 1 CATCH FRAMES: 1 UPDATES: 2241725 0 ( 0.0%) data values 34827 ( 1.6%) partial applications [2 in place, 34825 allocated new space] 2206898 ( 98.4%) updates to existing heap objects (46 by squeezing) UPD_CON_IN_NEW: 0: 0 0 0 0 0 0 0 0 0 UPD_PAP_IN_NEW: 34825: 0 0 0 34825 0 0 0 0 0 NEW GEN UPDATES: 2274700 ( 99.9%) OLD GEN UPDATES: 1852 ( 0.1%) Total bytes copied during GC: 190096 ************************************************** 3647137 ALLOC_HEAP_ctr 11882004 ALLOC_HEAP_tot 69647 ALLOC_FUN_ctr 69647 ALLOC_FUN_adm 69644 ALLOC_FUN_gds 34819 ALLOC_FUN_slp 34831 ALLOC_FUN_hst_0 34816 ALLOC_FUN_hst_1 0 ALLOC_FUN_hst_2 0 ALLOC_FUN_hst_3 0 ALLOC_FUN_hst_4 2382937 ALLOC_UP_THK_ctr 0 ALLOC_SE_THK_ctr 308906 ENT_IND_ctr 0 E!NT_PERM_IND_ctr requires +RTS -Z [... lots more info omitted ...] 0 GC_SEL_ABANDONED_ctr 0 GC_SEL_MINOR_ctr 0 GC_SEL_MAJOR_ctr 0 GC_FAILED_PROMOTION_ctr 47524 GC_WORDS_COPIED_ctr
The formatting of the information above the row of asterisks is subject to change, but hopefully provides a useful human-readable summary. Below the asterisks all counters maintained by the ticky-ticky system are dumped, in a format intended to be machine-readable: zero or more spaces, an integer, a space, the counter name, and a newline.
In fact, not all counters are
necessarily dumped; compile- or run-time flags can render certain
counters invalid. In this case, either the counter will simply
not appear, or it will appear with a modified counter name,
possibly along with an explanation for the omission (notice
ENT_PERM_IND_ctr
appears
with an inserted !
above). Software analysing
this output should always check that it has the counters it
expects. Also, beware: some of the counters can have
large values!