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NAME
cprof - A simple Call Count Profiling Tool using breakpoints for minimal runtime
performance impact.
DESCRIPTION
The cprof module is used to profile a program to find out how many times different
functions are called. Breakpoints similar to local call trace, but containing a counter,
are used to minimise runtime performance impact.
Since breakpoints are used there is no need for special compilation of any module to be
profiled. For now these breakpoints can only be set on BEAM code so BIFs cannot be call
count traced.
The size of the call counters is the host machine word size. One bit is used when pausing
the counter, so the maximum counter value for a 32-bit host is 2147483647.
The profiling result is delivered as a term containing a sorted list of entries, one per
module. Each module entry contains a sorted list of functions. The sorting order in both
cases is of decreasing call count.
Call count tracing is very lightweight compared to other forms of tracing since no trace
message has to be generated. Some measurements indicates performance degradation in the
vicinity of 10 percent.
EXPORTS
analyse() ->
{AllCallCount :: integer() >= 0,
ModAnalysisList :: mod_analysis_list()}
analyse(Limit) ->
{AllCallCount :: integer() >= 0,
ModAnalysisList :: mod_analysis_list()}
analyse(Mod) -> ModAnalysis :: mod_analysis()
analyse(Mod, Limit) -> ModAnalysis :: mod_analysis()
Types:
Mod = module()
Limit = integer() >= 0
mod_analysis_list() = [mod_analysis()]
mod_analysis() =
{Mod :: module(),
ModCallCount :: integer() >= 0,
FuncAnalysisList :: func_analysis_list()}
func_analysis_list() =
[{mfa(), FuncCallCount :: integer() >= 0}]
Collects and analyses the call counters presently in the node for either module
Mod, or for all modules (except cprof itself), and returns:
FuncAnalysisList:
A list of tuples, one for each function in a module, in decreasing
FuncCallCount order.
ModCallCount:
The sum of FuncCallCount values for all functions in module Mod.
AllCallCount:
The sum of ModCallCount values for all modules concerned in ModAnalysisList.
ModAnalysisList:
A list of tuples, one for each module except cprof, in decreasing ModCallCount
order.
If call counters are still running while analyse/0..2 is executing, you might get
an inconsistent result. This happens if the process executing analyse/0..2 gets
scheduled out so some other process can increment the counters that are being
analysed, Calling pause() before analysing takes care of the problem.
If the Mod argument is given, the result contains a ModAnalysis tuple for module
Mod only, otherwise the result contains one ModAnalysis tuple for all modules
returned from code:all_loaded() except cprof itself.
All functions with a FuncCallCount lower than Limit are excluded from
FuncAnalysisList. They are still included in ModCallCount, though. The default
value for Limit is 1.
pause() -> integer() >= 0
Pause call count tracing for all functions in all modules and stop it for all
functions in modules to be loaded. This is the same as
(pause({'_','_','_'})+stop({on_load})).
See also pause/1..3 below.
pause(FuncSpec) -> integer() >= 0
pause(Mod, Func) -> integer() >= 0
pause(Mod, Func, Arity) -> integer() >= 0
Types:
Mod = module()
Func = atom()
Arity = arity()
Pause call counters for matching functions in matching modules. The FS argument can
be used to specify the first argument to erlang:trace_pattern/3.
The call counters for all matching functions that has got call count breakpoints
are paused at their current count.
Return the number of matching functions that can have call count breakpoints, the
same as start/0..3 with the same arguments would have returned.
restart() -> integer() >= 0
restart(FuncSpec) -> integer() >= 0
restart(Mod, Func) -> integer() >= 0
restart(Mod, Func, Arity) -> integer() >= 0
Types:
Mod = module()
Func = atom()
Arity = arity()
Restart call counters for the matching functions in matching modules that are call
count traced. The FS argument can be used to specify the first argument to
erlang:trace_pattern/3.
The call counters for all matching functions that has got call count breakpoints
are set to zero and running.
Return the number of matching functions that can have call count breakpoints, the
same as start/0..3 with the same arguments would have returned.
start() -> integer() >= 0
Start call count tracing for all functions in all modules, and also for all
functions in modules to be loaded. This is the same as
(start({'_','_','_'})+start({on_load})).
See also start/1..3 below.
start(FuncSpec) -> integer() >= 0
start(Mod, Func) -> integer() >= 0
start(Mod, Func, Arity) -> integer() >= 0
Types:
Mod = module()
Func = atom()
Arity = arity()
Start call count tracing for matching functions in matching modules. The FS
argument can be used to specify the first argument to erlang:trace_pattern/3, for
example on_load.
Set call count breakpoints on the matching functions that has no call count
breakpoints. Call counters are set to zero and running for all matching functions.
Return the number of matching functions that has got call count breakpoints.
stop() -> integer() >= 0
Stop call count tracing for all functions in all modules, and also for all
functions in modules to be loaded. This is the same as
(stop({'_','_','_'})+stop({on_load})).
See also stop/1..3 below.
stop(FuncSpec) -> integer() >= 0
stop(Mod, Func) -> integer() >= 0
stop(Mod, Func, Arity) -> integer() >= 0
Types:
Mod = module()
Func = atom()
Arity = arity()
Stop call count tracing for matching functions in matching modules. The FS argument
can be used to specify the first argument to erlang:trace_pattern/3, for example
on_load.
Remove call count breakpoints from the matching functions that has call count
breakpoints.
Return the number of matching functions that can have call count breakpoints, the
same as start/0..3 with the same arguments would have returned.
SEE ALSO
eprof(3erl), fprof(3erl), erlang(3erl), User's Guide