Re: Concurrent code performance

Hi All C++ developers

I learned (from theory and practice) the most important benefit of
qualified multi-threaded programming is better performance.
Here it is a (not well-written) concurrent (two worker threads)
and sequential version
of Summation of [0, 2000000[ interval.
Of course my concurrent code is not good. It's for exposition only.

// concurrent code
#include <thread>
#include <iostream>

using namespace std;
long long s1 = 0, s2 = 0;
void Sum(int first, int last, long long& res) // calculate the sum in
[first, last[ interval
{
  while (first < last)
    res += first++;

}

int main()
{
  long long r1 = 0, r2 = 0;
  thread t1(Sum, 0, 1000000, std::ref(r1));
  thread t2(Sum, 1000000, 2000000, std::ref(r2));
  t1.join(); t2.join();
  cout << r1 + r2 << '\n';

  return 0;

}

// sequential code
#include <iostream>

using namespace std;
void Sum(int first, int last, long long& res) // calculate the sum in
[first, last[ interval
{
  while (first < last)
   res += first++;

}

int main()
{
  long long r = 0;
  Sum(0, 2000000, r);

  cout << r<< '\n';

  return 0;

}

I compiled and ran two codes using the following commands:
$ g++ -std=c++0x -pthread -pedantic -o2 concurrent_sum.c++ -o
concurrent_sum
$ g++ -std=c++0x -pedantic -o2 sequential_sum.c++ -o sequential_su=

$ time ./concurrent_sum
1999999999000
real 0m0.014s
user 0m0.016s
sys 0m0.004s
$ time ./sequential_sum
1999999999000
real 0m0.021s
user 0m0.020s
sys 0m0.000s
Of course the time command differs in several
execution, but honestly, I didn't see so much difference between two
execution.
In addition the generated code for sequential_sum is about 6 KB, but
the size
of concurrent_code is about 45 KB.
Is there any problem in my measurement? Why the concurrent object code
is 7+ times bigger than sequential version? How do you explain it?