VM上奇怪的程序延迟行为

我写了一个程序来读取256KB的数组以获得1ms的延迟。该程序非常简单和附加。但是，当我在Xen上的VM上运行它时，我发现延迟不稳定。时间单位为ms.

    #totalCycle CyclePerLine  totalms
    22583885 5513 6.452539
    3474342 848 0.992669
    3208486 783 0.916710
    25848572 6310 7.385306
    3225768 787 0.921648
    3210487 783 0.917282
    25974700 6341 7.421343
    3244891 792 0.927112
    3276027 799 0.936008
    25641513 6260 7.326147
    3531084 862 1.008881
    3233687 789 0.923911
    22397733 5468 6.399352
    3523403 860 1.006687
    3586178 875 1.024622
    26094384 6370 7.455538
    3540329 864 1.011523
    3812086 930 1.089167
    25907966 6325 7.402276

我认为一些过程正在做一些事情，它就像一个事件驱动的过程。有人遇到过这种情况吗?或者谁能指出可能实现这一点的潜在流程/服务?

下面是我的程序。我运行了1000次。每次都得到上面结果的一行。

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <ctime>
using namespace std;
#if defined(__i386__)
static __inline__ unsigned long long rdtsc(void)
{
    unsigned long long int x;
    __asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
    return x;
}
#elif defined(__x86_64__)
static __inline__ unsigned long long rdtsc(void)
{
    unsigned hi, lo;
    __asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi));
    return ( (unsigned long long)lo)|( ((unsigned long long)hi)<<32 );
}
#endif
#define CACHE_LINE_SIZE 64
#define WSS 24567 /* 24 Mb */
#define NUM_VARS WSS * 1024 / sizeof(long)
#define KHZ 3500000
// ./a.out memsize(in KB)
int main(int argc, char** argv)
{
    unsigned long wcet = atol(argv[1]);
    unsigned long mem_size_KB = 256;  // mem size in KB
    unsigned long mem_size_B  = mem_size_KB * 1024; // mem size in Byte
    unsigned long count       = mem_size_B / sizeof(long);
    unsigned long row         = mem_size_B / CACHE_LINE_SIZE;
    int           col         = CACHE_LINE_SIZE / sizeof(long);
    unsigned long long start, finish, dur1;
    unsigned long temp;
    long *buffer;
    buffer = new long[count];
    // init array
    for (unsigned long i = 0; i < count; ++i)
        buffer[i] = i;
    for (unsigned long i = row-1; i >0; --i) {
        temp = rand()%i;
        swap(buffer[i*col], buffer[temp*col]);
    }
    // warm the cache again
    temp = buffer[0];
    for (unsigned long i = 0; i < row-1; ++i) {
        temp = buffer[temp];
    }
    // First read, should be cache hit
    temp = buffer[0];
    start = rdtsc();
    int sum = 0;
    for(int wcet_i = 0; wcet_i < wcet; wcet_i++)
    {
        for(int j=0; j<21; j++)
        {
            for (unsigned long i = 0; i < row-1; ++i) {
                if (i%2 == 0) sum += buffer[temp];
                else sum -= buffer[temp];
                temp = buffer[temp];
            }
        }
    }
    finish = rdtsc();
    dur1 = finish-start;
    // Res
    printf("%lld %lld %.6fn", dur1, dur1/row, dur1*1.0/KHZ);
    delete[] buffer;
    return 0;
}