how slow is a mutex lock

mutex_test.cpp

/***************************************
Author:     Gabriel Espinoza
Desc:       They say lock-based concurrency is slow
            let's test how slow is slow
***************************************/
#include <iostream>
#include <mutex>
#include <functional>
#include <chrono>


using namespace std;
using namespace std::chrono;

class C {
    int x{};
    mutex m;
public:
    void inc(){x++;}
    void safe_inc(){
        lock_guard lk(m);
        x++;
    }
}c;

void run50000(function<void()> f)
{
    auto start = steady_clock::now();
    for( int i = 0; i < 50000; ++i)
    {
        f();
    }
    cout << "run time " << duration_cast<nanoseconds>(steady_clock::now() - start) << endl ; 
}

int main()
{
    cout <<"running inc()\n";
    run50000(bind(&C::inc,&c));
    cout <<"running safe_inc()\n";
    run50000(bind(&C::safe_inc,&c));

    return 0;
}