硬件：：Linux xxx 5.4.0-65-通用#Ubuntu x86_64 GNU/Linux CPU 1核心环境vwmare

软件线程：POLICY=SCHED_FIFO；参数.SCHED_PRIORITY=90；//最高优先级

unsigned long getUstime()
{
    struct timespec start_time;
    clock_gettime(CLOCK_MONOTONIC, &start_time);
    return start_time.tv_nsec/1000 + start_time.tv_sec*1e6;
}

# if 1

int  testclocktime()  {
    std::cout << "-----test clocktime------"<<std::endl;

    unsigned long long start = 0;
    unsigned long long end = 0;

    const static double  LOOP_TIMES = 100000.;
    double timesumCall = 0;
    for(int j = 0; j < 10; ++j) // loop1 million test;
    {
        volatile unsigned long long sum = 0;

        for(volatile  long i= 0; i< LOOP_TIMES; ++i)
        {
            start = getUstime(); // start time

            // test somethings

            end = getUstime(); // end time

            double now_diff =  end - start;  //calucate elapsed time
            sum += end - start;

            if(now_diff > 500) //judge
            {
                printf("overload 1000 us, now is %fn", now_diff);
            }
        }
        double times= sum / LOOP_TIMES;
        timesumCall+=times;
        printf("AVG_CYCLE : %lf us n", times);
    }

    timesumCall = timesumCall/10;
    printf("total AVG_CYCLE : %lf us n", timesumCall);

    return 0;
}

# endif

输出：

-----testclocktime------
AVG_CYCLE : 1.591390 us 
AVG_CYCLE : 1.586720 us 
AVG_CYCLE : 1.579920 us 
now diff time is 109.000000
now diff time is 104.000000
AVG_CYCLE : 1.580130 us 
AVG_CYCLE : 1.581860 us 
now diff time is 114.000000
now diff time is 101.000000
now diff time is 104.000000
AVG_CYCLE : 1.584920 us 
now diff time is 106.000000
now diff time is 51880.000000
AVG_CYCLE : 2.102190 us 
now diff time is 106.000000
AVG_CYCLE : 1.563000 us 
AVG_CYCLE : 1.596560 us 
AVG_CYCLE : 1.579730 us 
total AVG_CYCLE : 1.634642 us 
total Maxrdtime : 51880.000000 us

如输出所示，在程序中，正常运行时间约为2us，平均时间在2us以内，但在循环过程中会出现大于100us的时间跳跃。

我已经在执行函数中将线程优先级设置为最高级别，并将线程调度模式设置为FIFO。

为什么会发生这种事？或者这样说，如果我确保在实时线程中执行函数时没有抖动，会怎么样？