cprof

2002 2016 Ericsson AB, All Rights Reserved Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. The Initial Developer of the Original Code is Ericsson AB. cprof Raimo Niskanen nobody nobody 2002-09-12 PA1 cprof.sgml

cprof A simple Call Count Profiling Tool using breakpoints for minimal runtime performance impact.

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 s 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.

analyse() -> {AllCallCount, ModAnalysisList} analyse(Limit) -> {AllCallCount, ModAnalysisList} analyse(Mod) -> ModAnalysis analyse(Mod, Limit) -> ModAnalysis Collect and analyse call counters. Limit = integer() Mod = atom() AllCallCount = integer() ModAnalysisList = [ModAnalysis] ModAnalysis = {Mod, ModCallCount, FuncAnalysisList} ModCallCount = integer() FuncAnalysisList = [{{Mod, Func, Arity}, FuncCallCount}] Func = atom() Arity = integer() FuncCallCount = integer()

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() Pause running call count trace for all functions.

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})).