clock_gettime CLOCK_REALTIME意外结果

Question

我想看看管道处理数据需要多长时间，我存储了

的结果

clock_gettime (CLOCK_REALTIME, &start);

当我将数据项添加到输入缓冲区时。

然后，当我计算处理该项目所需的时间时，我会使用该时间。

对于前几个项似乎没问题，但之后我得到了疯狂的结果。

我计算出使用此功能所用的时间

double xelapsed (struct timespec a, struct timespec b)
{
   return (a.tv_sec - b.tv_sec) * 1000000.0
          + (a.tv_nsec - b.tv_nsec) / 1000.0;
}

这就是我最终的结果：

bash-4.1$ ./pipe
Latency: 1.447000 μs
Latency: 81.549000  μs
Latency: 104.253000  μs
Latency: 112.497000  μs
Latency: 121.307000  μs
Latency: 128.993000  μs
Latency: 136.334000  μs
Latency: 143.237000  μs
Latency: 147.910000  μs
Latency: 152.242000  μs
Latency: 156.492000  μs
Latency: 160.729000  μs
Latency: 164.793000  μs
Latency: 168.782000  μs
Latency: 172.756000  μs
Latency: 176.720000  μs
Latency: 175.370000  μs
Latency: 184.937000  μs
Latency: 183.424000  μs
Latency: 187.353000  μs
Latency: 196.870000  μs
Latency: 200.874000  μs
Latency: 205.332000  μs
Latency: 209.353000  μs
Latency: 213.677000  μs
Latency: 218.040000  μs
Latency: 222.435000  μs
Latency: 226.559000  μs
Latency: 230.897000  μs
Latency: 235.170000  μs
Latency: 239.481000  μs
Latency: 243.829000  μs
Latency: 247.709000  μs
Latency: 251.974000  μs
Latency: 256.338000  μs
Latency: 260.363000  μs
Latency: 264.832000  μs
Latency: 269.293000  μs
Latency: 273.171000  μs
Latency: 277.525000  μs
Latency: 281.701000  μs
Latency: 285.674000  μs
Latency: 290.187000  μs
Latency: 294.239000  μs
Latency: 298.504000  μs
Latency: 302.604000  μs
Latency: 307.095000  μs
Latency: 310.792000  μs
Latency: 315.343000  μs
Latency: 318.812000  μs
Latency: 322.721000  μs
Latency: 327.149000  μs
Latency: 331.065000  μs
Latency: 335.114000  μs
Latency: 339.632000  μs
Latency: 342.989000  μs
Latency: 344.433000  μs
Latency: 348.567000  μs
Latency: 352.376000  μs
Latency: 356.801000  μs
Latency: 360.752000  μs
Latency: 364.337000  μs
Latency: 368.808000  μs
Latency: 372.082000  μs
Latency: 376.500000  μs
Latency: 380.283000  μs
Latency: 384.611000  μs
Latency: 388.134000  μs
Latency: 392.083000  μs
Latency: 396.484000  μs
Latency: 400.428000  μs
Latency: 1426625359409111.000000  μs
Latency: 1426625359409117.250000  μs
Latency: 1426625359409123.250000  μs
Latency: 1426625359409128.750000  μs
Latency: 1426625359409134.500000  μs
Latency: 1426625359409140.500000  μs
Latency: 1426625359409146.000000  μs
Latency: 1426625359409151.750000  μs
Latency: 1426625359409157.500000  μs
Latency: 1426625359409163.000000  μs
Latency: 1426625359409168.500000  μs
Latency: 1426625359409174.250000  μs
Latency: 1426625359409180.000000  μs
Latency: 1426625359409185.500000  μs
Latency: 1426625359409191.000000  μs
Latency: 1426625359409196.750000  μs
Latency: 1426625359409202.250000  μs