问题描述

我的意思是:我如何测量我的 CPU 花在函数执行上的时间以及运行我的函数所需的挂钟时间?(我对 Linux/Windows 以及 x86 和 x86_64 感兴趣).看看我想做什么(我在这里使用 C++，但我更喜欢 C 解决方案):

I mean: how can I measure time my CPU spent on function execution and wall clock time it takes to run my function? (Im interested in Linux/Windows and both x86 and x86_64). See what I want to do (Im using C++ here but I would prefer C solution):

int startcputime, endcputime, wcts, wcte;

startcputime = cputime();
function(args);
endcputime = cputime();

std::cout << "it took " << endcputime - startcputime << " s of CPU to execute this
";

wcts = wallclocktime();
function(args);
wcte = wallclocktime();

std::cout << "it took " << wcte - wcts << " s of real time to execute this
";

另一个重要问题:这种时间测量架构是否独立?

推荐答案

这是一个适用于 Windows 和 Linux 以及 C 和 C++ 的复制粘贴解决方案.

Here's a copy-paste solution that works on both Windows and Linux as well as C and C++.

正如评论中提到的，有一个 boost 库可以做到这一点.但是如果你不能使用 boost，这应该可以工作:

As mentioned in the comments, there's a boost library that does this. But if you can't use boost, this should work:

//  Windows
#ifdef _WIN32
#include <Windows.h>
double get_wall_time(){
    LARGE_INTEGER time,freq;
    if (!QueryPerformanceFrequency(&freq)){
        //  Handle error
        return 0;
    }
    if (!QueryPerformanceCounter(&time)){
        //  Handle error
        return 0;
    }
    return (double)time.QuadPart / freq.QuadPart;
}
double get_cpu_time(){
    FILETIME a,b,c,d;
    if (GetProcessTimes(GetCurrentProcess(),&a,&b,&c,&d) != 0){
        //  Returns total user time.
        //  Can be tweaked to include kernel times as well.
        return
            (double)(d.dwLowDateTime |
            ((unsigned long long)d.dwHighDateTime << 32)) * 0.0000001;
    }else{
        //  Handle error
        return 0;
    }
}

//  Posix/Linux
#else
#include <time.h>
#include <sys/time.h>
double get_wall_time(){
    struct timeval time;
    if (gettimeofday(&time,NULL)){
        //  Handle error
        return 0;
    }
    return (double)time.tv_sec + (double)time.tv_usec * .000001;
}
double get_cpu_time(){
    return (double)clock() / CLOCKS_PER_SEC;
}
#endif

有很多方法可以实现这些时钟.但上面的代码片段使用的是:

There's a bunch of ways to implement these clocks. But here's what the above snippet uses:

对于 Windows:

For Windows:

• Wall Time:性能计数器
• CPU 时间:GetProcessTimes()

对于 Linux:

• Wall Time:gettimeofday()
• CPU 时间:clock()

这是一个小演示:

#include <math.h>
#include <iostream>
using namespace std;

int main(){

    //  Start Timers
    double wall0 = get_wall_time();
    double cpu0  = get_cpu_time();

    //  Perform some computation.
    double sum = 0;
#pragma omp parallel for reduction(+ : sum)
    for (long long i = 1; i < 10000000000; i++){
        sum += log((double)i);
    }

    //  Stop timers
    double wall1 = get_wall_time();
    double cpu1  = get_cpu_time();

    cout << "Wall Time = " << wall1 - wall0 << endl;
    cout << "CPU Time  = " << cpu1  - cpu0  << endl;

    //  Prevent Code Elimination
    cout << endl;
    cout << "Sum = " << sum << endl;

}

输出(12 个线程):

Output (12 threads):

Wall Time = 15.7586
CPU Time  = 178.719

Sum = 2.20259e+011

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