使用clock（）衡量执行​​时间 [英] Using clock() to measure execution time

问题描述

我正在使用GCC和专有的DSP交叉编译器运行C程序，以模拟某些功能。我正在使用以下代码来衡量程序特定部分的执行时间：

I am running a C program using GCC and a proprietary DSP cross-compiler to simulate some functioality. I am using the following code to measure the execution time of particular part of my program:

clock_t start,end;
printf("DECODING DATA:\n");
start=clock();
conv3_dec(encoded, decoded,3*length,0);
end=clock();
duration = (double)(end - start) / CLOCKS_PER_SEC;
printf("DECODING TIME = %f\n",duration);

其中 conv3_dec（）是定义的函数

现在，事情是当我的程序运行时， conv3_dec（） 函数运行将近2个小时，但 printf（ DECODING TIME =％f\n，duration）的输出表示执行的功能仅需半秒即可完成（ DECODING TIME = 0.455443 ）。

Now the thing is when my program runs, the conv3_dec() functions runs for almost 2 hours but the output from the printf("DECODING TIME = %f\n",duration) says that the execution of the function finished in just half a second (DECODING TIME = 0.455443) . This is very confusing for me.

我以前使用 clock_t 技术来测量程序的运行时间，但是差异从未如此巨大。这是由交叉编译器引起的吗？顺便提一句，模拟器仿真的DSP处理器仅以500MHz运行，因此DSP处理器和我的CPU的时钟速度之间的差异也是如此，这导致错误正在测量CLOCKS_PER_SEC。

I have used the clock_t technique to measure the runtimes of programs previously but the difference has never been so huge. Is this being caused by the cross-compiler. Just as a side note, the simulator simulates a DSP processor running at just 500MHz, so is the difference in the clock speeds of the DSP processor and my CPU causing the error is measuring the CLOCKS_PER_SEC.

推荐答案

对于两个小时的时间段，我不会太担心 clock（），它对于测量亚秒级的持续时间要有用得多。

For durations like two hours, I wouldn't be too concerned about clock(), it's far more useful for measuring sub-second durations.

只需使用 time（）如果您想要实际经过的时间，则类似于（缺少的虚拟物品）：

Just use time() if you want the actual elapsed time, something like (dummy stuff supplied for what was missing):

#include <stdio.h>
#include <time.h>

// Dummy stuff starts here
#include <unistd.h>
#define encoded 0
#define decoded 0
#define length 0
static void conv3_dec (int a, int b, int c, int d) {
    sleep (20);
}
// Dummy stuff ends here

int main (void) {
    time_t start, end, duration;
    puts ("DECODING DATA:");
    start = time (0);
    conv3_dec (encoded, decoded, 3 * length, 0);
    end = time (0);
    duration = end - start;
    printf ("DECODING TIME = %d\n", duration);
    return 0;
}

会生成：

DECODING DATA:
DECODING TIME = 20

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