为什么相同的向量v1（正常情况下）和v2（带有std：：execution：parallel）对于v1花费的时间较少，而对于v2花费的时间较多？
我原以为并行排序会更快完成。

#include <iostream>
#include <vector>
#include <chrono>
#include <algorithm>
#include <execution>

using namespace std;

int main() {

    // Generate identical vectors v1 and v2 of length N
    // and fill them with v[i] = i/200;
    int N = 10000;
    vector<int> v1(N);
    for(int i=0; i<N; i++) v1[i] = i/200;
    auto v2 = v1;

    // Calculate the time taken to sort in serial way.
    auto start = std::chrono::system_clock::now();
    sort(v1.begin(), v1.end());
    auto end = std::chrono::system_clock::now();
    auto diff = end - start;
    cout << diff.count() << " = serial count" << endl;

    // Calculate the time taken to sort in parallel way using
    // std::execution::par
    start = std::chrono::system_clock::now();
    sort(std::execution::par, v2.begin(), v2.end());
    end = std::chrono::system_clock::now();
    diff = end - start;
    cout << diff.count() << " = parallel parallel" << endl;

    return 0;
}

结果：

626600 = serial count
1048100 = parallel count