Profiling is done in the following steps:
Functions can be specified as either all in the system, all in one module, all arities of one function, one function, or all functions in all modules not yet loaded. As for now, BIFs cannot be call count traced.
The analysis result can either be for all modules, or for one
module. In either case a call count limit can be given to filter
out the functions with a call count below the limit. The all
modules analysis does not contain the module
Call count tracing is very lightweight compared to other forms of tracing since no trace message has to be generated. Some measurements indicates performance degradations in the vicinity of 10 percent.
The following sections show some examples of profiling with
From the Erlang shell:
1> cprof:start(), cprof:pause(). % Stop counters just after start
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2> cprof:analyse().
{30,
[{erl_eval,11,
[{{erl_eval,expr,3},3},
{{erl_eval,'-merge_bindings/2-fun-0-',2},2},
{{erl_eval,expand_module_name,2},1},
{{erl_eval,merge_bindings,2},1},
{{erl_eval,binding,2},1},
{{erl_eval,expr_list,5},1},
{{erl_eval,expr_list,3},1},
{{erl_eval,exprs,4},1}]},
{orddict,8,
[{{orddict,find,2},6},
{{orddict,dict_to_list,1},1},
{{orddict,to_list,1},1}]},
{packages,7,[{{packages,is_segmented_1,1},6},
{{packages,is_segmented,1},1}]},
{lists,4,[{{lists,foldl,3},3},{{lists,reverse,1},1}]}]}
3> cprof:analyse(cprof).
{cprof,3,[{{cprof,tr,2},2},{{cprof,pause,0},1}]}
4> cprof:stop().
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The example showed the background work that the shell performs
just to interpret the first command line. Most work is done by
What is captured in this example is the part of the work the
shell does while interpreting the command line that occurs
between the actual calls to
From the Erlang shell:
1> cprof:start(),R=calendar:day_of_the_week(1896,4,27),cprof:pause(),R.
1
2> cprof:analyse(calendar).
{calendar,9,
[{{calendar,df,2},1},
{{calendar,dm,1},1},
{{calendar,dy,1},1},
{{calendar,last_day_of_the_month1,2},1},
{{calendar,last_day_of_the_month,2},1},
{{calendar,is_leap_year1,1},1},
{{calendar,is_leap_year,1},1},
{{calendar,day_of_the_week,3},1},
{{calendar,date_to_gregorian_days,3},1}]}
3> cprof:stop().
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The example tells us that "Aktiebolaget LM Ericsson & Co"
was registered on a Monday (since the return value
of the first command is 1), and that the
Using
Write a module:
-module(sort).
-export([do/1]).
do(N) ->
cprof:stop(),
cprof:start(),
do(N, []).
do(0, L) ->
R = lists:sort(L),
cprof:pause(),
R;
do(N, L) ->
do(N-1, [random:uniform(256)-1 | L]).
From the Erlang shell:
1> c(sort).
{ok,sort}
2> l(random).
{module,random}
3> sort:do(1000).
[0,0,1,1,1,1,1,1,2,2,2,3,3,3,3,3,4,4,4,5,5,5,5,6,6,6,6,6,6|...]
4> cprof:analyse().
{9050,
[{lists_sort,6047,
[{{lists_sort,merge3_2,6},923},
{{lists_sort,merge3_1,6},879},
{{lists_sort,split_2,5},661},
{{lists_sort,rmerge3_1,6},580},
{{lists_sort,rmerge3_2,6},543},
{{lists_sort,merge3_12_3,6},531},
{{lists_sort,merge3_21_3,6},383},
{{lists_sort,split_2_1,6},338},
{{lists_sort,rmerge3_21_3,6},299},
{{lists_sort,rmerge3_12_3,6},205},
{{lists_sort,rmerge2_2,4},180},
{{lists_sort,rmerge2_1,4},171},
{{lists_sort,merge2_1,4},127},
{{lists_sort,merge2_2,4},121},
{{lists_sort,mergel,2},79},
{{lists_sort,rmergel,2},27}]},
{random,2001,
[{{random,uniform,1},1000},
{{random,uniform,0},1000},
{{random,seed0,0},1}]},
{sort,1001,[{{sort,do,2},1001}]},
{lists,1,[{{lists,sort,1},1}]}]}
5> cprof:stop().
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The example shows some details of how
This time, since the shell was not involved, no other work was
done in the system during the profiling. If you retry the same
example with a freshly started Erlang emulator, but omit the
command