Assistance with C++ program profiling

Question

I really want to know how much time different routines take in my application. I am using GCC 3.4.2 with Dev-C++ IDE and gprof for profiling. Here is the begining of the result file:

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
  7.48      0.89     0.89                             __gnu_cxx::__exchange_and_add(int volatile*, int)
  7.39      1.77     0.88                             _Unwind_SjLj_Register
  6.22      2.51     0.74                             _Unwind_SjLj_Unregister
  3.70      2.95     0.44  2425048     0.00     0.00  rt::wctree_node<std::vector<OPT_Inst, std::allocator<OPT_Inst> > >::get(std::string, bool&)
  3.28      3.34     0.39                             std::string::operator[](unsigned int)
  3.11      3.71     0.37                             std::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string()
  2.86      4.05     0.34                             std::string::_M_mutate(unsigned int, unsigned int, unsigned int)
  2.69      4.37     0.32                             __gnu_cxx::__atomic_add(int volatile*, int)
  2.61      4.68     0.31    38655     0.00     0.00  SPSBase::containerBoxFillSet(double, double, double, double)

Can someone explain to me the first ones except rt::wctree (that are obviously not made by me), where do they come from and what is their goal in the program?

Matthieu M. Matthieu M. · Accepted Answer · 2012-07-14T16:17:08

The two _Unwind look to me like exception handling.

The _M_mutate seems to indicate that you are copying strings (detail of implementation of the Copy on Write behavior of libstdc++ implementation) which seems to be underlined by the presence of the string destructor in the profile.

I guess the atomic operations also come from the string COW behavior, since the internal buffer is reference counted.

So it seems the bulk of your time is spent copying std::string around.

EDIT: okay, so now look at your rt::wctree<>::get(std::string, bool&). The parameter is passed by copy. 2425048 calls, 2425048 copies. Why don't you try a const& here ?

Assistance with C++ program profiling

1 Answers