gprof を触りだけ

gprofとは

プロファイラ．

参考

https://www.howtoforge.com/tutorial/how-to-install-and-use-profiling-tool-gprof/

環境

paiza cloud．

~$ g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
~$ gprof --version
GNU gprof (GNU Binutils for Ubuntu) 2.26.1
Based on BSD gprof, copyright 1983 Regents of the University of California.
This program is free software.  This program has absolutely no warranty.

(bash on ubuntu) は関数がうまく拾えないのか，何も表示されませんでした．(バージョン違いかも？)

.

install

apt install binutils

use

適当なプログラムがあったとする．hoge.cpp．

#include <bits/stdc++.h>
using namespace std;

int func1(){
    int x = 0;
    for (int i = 0; i < 10101010; ++i){
        x += i; x %= 107;
    }
    return x;
}

int func2(){
    int x = 0;
    for (int i = 0; i < 40101010; ++i){
        x *= i; x %= 107;
    }
    return x;
}

int func3(){
    int y = 0;
    for (int i = 0; i < 4; ++i){
        y += func1();
    }
    return y;
}

int main(){
    func1();
    func2();
    func3();
    return 0;
}

-pg をつける

g++ hoge.cpp -pg

-pg を付けてコンパイルしたファイルを実行すると，gmon.out を生成する．

a.outとgmon.outをgprofに渡す．

~$ gprof a.out gmon.out
Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 56.36      0.43     0.43        5    86.79    86.79  func1()
 44.56      0.78     0.34        1   343.12   343.12  func2()
  0.00      0.78     0.00        1     0.00     0.00  _GLOBAL__sub_I__Z5func1v
  0.00      0.78     0.00        1     0.00     0.00  __static_initialization_and_destruction_0(int, int)
  0.00      0.78     0.00        1     0.00   347.16  func3()
以下続く

関数単位で表示されるので，例えば

#include <bits/stdc++.h>
using namespace std;

int main(){
    int x = 0;
    for (int i = 0; i < 10101010; ++i)
        x += i; x %= 107;
    for (int i = 0; i < 40101010; ++i)
        x *= i; x %= 107;
    for (int j = 0; j < 4; ++j)
        for (int i = 0; i < 10101010; ++i)
            x += i; x %= 107;
    
    return 0;
}

なコードを与えると，

  %   cumulative   self              self     total
 time   seconds   seconds    calls  Ts/call  Ts/call  name
 95.90      0.29     0.29                             main
  0.00      0.29     0.00        1     0.00     0.00  _GLOBAL__sub_I_main
  0.00      0.29     0.00        1     0.00     0.00  __static_initialization_and_destruction_0(int, int)

はい．

-O3 -O2 を付けても行方不明になることがある．

~$ g++ hoge.cpp -pg -O3
~$ ./a.out
10
0
40
~$ gprof a.out gmon.out | head -n 20
Flat profile:

Each sample counts as 0.01 seconds.
 no time accumulated

  %   cumulative   self              self     total
 time   seconds   seconds    calls  Ts/call  Ts/call  name
  0.00      0.00     0.00        1     0.00     0.00  _GLOBAL__sub_I__Z5func1v

 %         the percentage of the total running time of the
time       program used by this function.

cumulative a running sum of the number of seconds accounted
 seconds   for by this function and those listed above it.

 self      the number of seconds accounted for by this
seconds    function alone.  This is the major sort for this
           listing.

calls      the number of times this function was invoked, if

気持ち

使い慣れない…