Profiling time elapse of array access using rdtscll in a kernel module

Hi, I am trying to profile the time elapse of accessing an integer array using rdtscll. I wrote a user-mode program and a kernel module doing the same work. The results from rdtsc however look pretty odd. The machine is an Intel xeon 3.1Ghz box. The user-mode program is Code: unsigned long long ini, end; int dummy; /* Initialize a 6144KB integer array */ .. ... gettimeofday(&start_tv, &tz); ini = rdtsc(); for (i = 0; i < array_element; i++) { dummy = int_array[j]; } end = rdtsc(); gettimeofday(&end_tv, &tz1); .. ... printf("Time elapse %llu cycles\n", end-ini); printf("Time elapse in %lf usec\n", ....); So I got the output of ini: 2032056902618536, end: 2032056914493232 Time elapse 11874696 cycles Time elapse in 3769.000000 usec These number looks reasonable. However, when I use the same logic in my kernel module which has the following code Code: data_array = (int *)vmalloc(6144KB); for(i = 0; i < 6144KB/sizeof(int); i++) { data_array[i] = random32() % 1000;} rdtscll(ini); for(i = 0; i < nr_elements; i++) {     val = data_array[i]; } rdtscll(end); printk("ini: %llu, end: %llu\n", ini, end); printk("TIme elapse %llu\n", end - ini); The outputs are ini: 2031745377590838, end: 2031745377591152 data array access is 314. So it only takes about 314 CPU cycles to traverse the 6144KB size array, which should not be correct. Assuming that in an ideal case the CPU uses 1 cycle to load the integer from on-chip cache, and the total number of integer of 6144KB array is 1572864, which is much greater than 314. As the user-mode time elapse (11874696 cycles) looks reasonable, I am wondering is there anything wrong in my kernel module. Any suggestion is welcome. Thanks in advance.

URL: