Gprof gives no result

Question

I am trying to use gprof to profile some numerical code that I am developing, but gprof does not seem to collect data from my program. Here is my command line:

g++ -Wall -O3 -g -pg -o fftw_test fftw_test.cpp -lfftw3 -lfftw3_threads -lm && ./fftw_test

The gmon.out file is created, but it has no data. When i started

gprof -b fftw_test gmon.out > gprof.out

All I get is

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  Ts/call  Ts/call  name    


                        Call graph


granularity: each sample hit covers 2 byte(s) no time propagated

index % time    self  children    called     name


Index by function name

Any ideas?

The code has a lot of things, it does not just call FFTW routines. It has functions that calculate certain complex coefficients, functions that multiply input data by these coefficients, etc.

Edit: Includes sample code and results.

#include <cstdlib>
#include <ctime>

int main()
{
   std::srand( std::time( 0 ) );

   double sum = 0.0;

   for ( int i = 0; i < RAND_MAX; ++i )
      sum += std::rand() / ( double ) RAND_MAX;

   std::cout << sum << '\n';

   return 0;
}

Command lines:

$ g++ -Wall -O3 -g -pg -o gprof_test gprof_test.cpp && ./gprof_test
1.07374e+09
$ gprof -b gprof_test gmon.out > gprof.out
$ cat gprof.out

Result:

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    


                        Call graph


granularity: each sample hit covers 2 byte(s) no time propagated

index % time    self  children    called     name


Index by function name

What is it.

Answer 1

gprof does not seem to be able to collect data from my program. Here is my command line:

g++ -Wall -O3 -g -pg -o fftw_test fftw_test.cpp -lfftw3 -lfftw3_threads -lm && ./fftw_test

fftw , , fftw. ? gprof. . gprof, gprof.

GNU gprof . -, c/cpp, -pg ( mcount - https://en.wikipedia.org/wiki/Gprof) - / . -, , , , . (setitimer). Setitimer 10 1 (100 1000 ).

fftw, , , mcount. - , (https://en.wikipedia.org/wiki/Gprof - " " ).

perf mcount ( / -g), / ( PMU), 100 1000 , () . perf record -F1000 ./fftw_test ( 1 ) perf report perf report > report.txt. GUI/HTML : https://github.com/KDAB/hotspot <3 >

setitimer google-perftools https://github.com/gperftools/gperftools "CPU PROFILER".

======

gprof Debian 8.6 Linux 3.16.0-4-amd64 x86_64, g++ (Debian 4.9.2-10), gprof - "GNU gprof (GNU Binutils Debian) 2.27"

$ cat gprof_test.cpp
#include <cstdlib>
#include <ctime>
#include <iostream>
int main()
{
   std::srand( std::time( 0 ) );
   double sum = 0.0;
   for ( int i = 0; i < 100000000; ++i )
      sum += std::rand() / ( double ) RAND_MAX;
   std::cout << sum << '\n';
   return 0;
}
$ g++ -Wall -O3 -g -pg -o gprof_test gprof_test.cpp && time ./gprof_test
5.00069e+06
real    0m0.992s
$ gprof -b gprof_test gmon.out
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_main

, gprof 1- ( -pg). - gprof, ( 0,72 2- ):

$ cat *cpp
#include <cstdlib>
#include <ctime>
#include <iostream>

int rand_wrapper1()
{
  return std::rand();
}
int rand_scale1()
{
  return rand_wrapper1() / ( double ) RAND_MAX;
}
int main()
{
   std::srand( std::time( 0 ) );
   double sum = 0.0;
   for ( int i = 0; i < 100000000; ++i )
    sum+= rand_scale1();
//      sum += std::rand() / ( double ) RAND_MAX;
   std::cout << sum << '\n';
   return 0;
}
$ g++ -Wall -O3 -fno-inline -g -pg -o gprof_test gprof_test.cpp && time ./gprof_test
real    0m2.345s
$ gprof -b gprof_test gmon.out
Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ns/call  ns/call  name
 80.02      0.57     0.57                             rand_scale1()
 19.29      0.71     0.14 100000000     1.37     1.37  rand_wrapper1()
  2.14      0.72     0.02                             frame_dummy
  0.00      0.72     0.00        1     0.00     0.00  _GLOBAL__sub_I__Z13rand_wrapper1v
  0.00      0.72     0.00        1     0.00     0.00  __static_initialization_and_destruction_0(int, int) [clone .constprop.0]


                        Call graph


granularity: each sample hit covers 2 byte(s) for 1.39% of 0.72 seconds

index % time    self  children    called     name
                                                 <spontaneous>
[1]     97.9    0.57    0.14                 rand_scale1() [1]
                0.14    0.00 100000000/100000000     rand_wrapper1() [2]
-----------------------------------------------
                0.14    0.00 100000000/100000000     rand_scale1() [1]
[2]     19.0    0.14    0.00 100000000         rand_wrapper1() [2]

:

$ perf record ./gprof_test
0
[ perf record: Woken up 2 times to write data ]
[ perf record: Captured and wrote 0.388 MB perf.data (~16954 samples) ]
$ perf report |more   
# Samples: 9K of event 'cycles'
# Event count (approx.): 7373484231
#
# Overhead     Command      Shared Object                     Symbol
# ........  ..........  .................  .........................
#
    25.91%  gprof_test  gprof_test         [.] rand_scale1()
    21.65%  gprof_test  libc-2.19.so       [.] __mcount_internal
    13.88%  gprof_test  libc-2.19.so       [.] _mcount
    12.54%  gprof_test  gprof_test         [.] main
     9.35%  gprof_test  libc-2.19.so       [.] __random_r
     8.40%  gprof_test  libc-2.19.so       [.] __random
     3.97%  gprof_test  gprof_test         [.] rand_wrapper1()
     2.79%  gprof_test  libc-2.19.so       [.] rand
     1.41%  gprof_test  gprof_test         [.] mcount@plt
     0.03%  gprof_test  [kernel.kallsyms]  [k] memset