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

Subject: Re: [Boost-users] boost::function performance issues with C++11
From: Ben Pope (benpope81_at_[hidden])
Date: 2014-07-09 00:05:48

On Tuesday, July 08, 2014 06:11 PM, Adam Romanek wrote:
>
> As promised I performed a simple test during the weekend and wasn't able
> to reproduce the issue. See the code below:
>
> ---
> #include <vector>
> #include <boost/bind.hpp>
> #include <boost/function.hpp>
>
> void call(boost::function<int ()> f) {
>    f();
> }
>
> long long total = 0;
>
> int func2(std::vector<int> i){
>      total += i.size();
>      return i.size();
> }
>
> int main() {
>      std::vector<int> v(100);
>      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();
> }
> ---
>
> The performance does not change when compiling with -std=c++11 or
> without it. I compile the code like this:
>
> $ g++ -I/home/A.Romanek/tmp/boost/boost_1_55_0 main.cpp -std=c++11 -O2
> && time ./a.out
>
> real    0m1.669s
>
> My setup is Ubuntu 14.04, gcc 4.8.2 and my CPU is Intel Core2Duo P8700 @
> 2.53GHz.
>
> Could you please provide a complete example so that I could reproduce
> the issue on my desk?

Make of this what you will, I used your example:

g++-4.8.2
        -std=c++03	-std=c++11
real	0m0.753s	0m0.798s
user	0m0.752s	0m0.797s
sys	0m0.001s	0m0.002s

g++-4.9
        -std=c++03	-std=c++11
real	0m0.786s	0m1.419s
user	0m0.785s	0m1.418s
sys	0m0.001s	0m0.002s

clang++-3.4 (libstdc++ from g++-4.9)
        -std=c++03	-std=c++11
real	0m0.799s	0m1.407s
user	0m0.798s	0m1.406s
sys	0m0.001s	0m0.002s

clang++-3.4 (libc++ trunk)
-std=c++03		-std=c++11
real	0m1.382s	0m1.389s
user	0m1.381s	0m1.387s
sys	0m0.002s	0m0.002s

clang++-3.5 (libstdc++ from g++-4.9)
-std=c++03		-std=c++11
real	0m0.812s	0m1.112s
user	0m0.811s	0m1.111s
sys	0m0.002s	0m0.002s

clang++-3.5 (libc++ trunk)
-std=c++03		-std=c++11
real	0m0.782s	0m0.770s
user	0m0.781s	0m0.769s
sys	0m0.002s	0m0.002s

Ben