Re: [Boost-users] boost::function performance issues with C++11

Subject: Re: [Boost-users] boost::function performance issues with C++11
From: Adam Romanek (romanek.adam_at_[hidden])
Date: 2014-07-04 08:10:46

On 03.07.2014 23:10, 饭桶 wrote:
> Hi,
>
> Does anyone know why -std=c++11 causes so much difference on
> boost::function?
>
> I was planed to understand if there any performance issues with big size
> of parameters.
> So I wrote a function that takes a vector as parameter, like func2
> shows. I know it's better to use a pointer or reference as function
> parameter. I just want to evaluate the performance, so let's keep the
> vector as parameter.
>
> However, I found that it's quite slow when compiled with -std=c++11. In
> detail, it takes 173874 milliseconds with C++11, while it takes 3676
> seconds without C++11.
>
> About 50 times slower!! How can that be?
>
> In my opinion, I thought boost::function should had the same performance
> with std::function. So I decided to try std::function in C++11 directly,
> Finally, it takes about 29233 milliseconds. That's till 8 times slows!
>
> Can anyone tell me what happend here?
>
> int func2(std::vector<int> i){
>      total += i.size();
>      return i.size();
> }
>
>      const int T = 1000000;
>      s = boost::chrono::system_clock::now();
>      for (int i = 0; i < T; ++i)
>          call(boost::bind(&func2, v));
>      e = boost::chrono::system_clock::now();
>
> In case you need to know my enviorment, my OS is Arch, compiler is gcc
> 4.9.0, and optimizations are default.
> The execution time (ms) of three versions I tried:
> boost::function with C++11 : 173874
> boost::function without C++11 : 3676
> std::function in C++11 : 29233
>
> Any thoughts are appreciated!

Hi!

I'd run the example code through Callgrind (valgrind --tool=callgrind) 
and then compare the reports in KCachegrind. This should at least give 
you an idea of the source of the problem.

I may do that myself during the weekend in case you would not able to do 
that on your own.

WBR,
Adam Romanek