After reading this article, I tried to reproduce the example on my Mac. However, my curve for the first example looks completely different, and I don’t understand why ..
My code is below:
#include <mach/mach_time.h>
#include <time.h>
#include <stdio.h>
#include <stdlib.h>
void mach_absolute_difference(uint64_t end, uint64_t start, struct timespec *tp) {
uint64_t difference = end - start;
static mach_timebase_info_data_t info = {0,0};
if (info.denom == 0)
mach_timebase_info(&info);
uint64_t elapsednano = difference * (info.numer / info.denom);
tp->tv_sec = elapsednano * 1e-9;
tp->tv_nsec = elapsednano - (tp->tv_sec * 1e9);
}
int main(void)
{
int len = 64 * 1024 * 1024;
int *arr = (int *)malloc(sizeof(int)*len);
uint64_t start,end;
struct timespec tp;
start = mach_absolute_time();
for (int i = 0; i <len; i += K)
arr[i] = 0;
end = mach_absolute_time();
mach_absolute_difference(end, start, &tp);
FILE *fp;
fp=fopen("simple_array.log", "a+");
fprintf(fp, "%i\t%ld\t%ld\n", K, tp.tv_sec,
tp.tv_nsec);
fclose(fp);
free(arr);
return 0;
}
I measured the time described in this blog , hoping it would be correct. I am also wondering what should I use to measure runtime or CPU cycles on a Mac. Or it would even be nicer to see the number of hits / skips of the cache for a particular function. However, Shark only shows percentages of l2 cache misses.
Update this when compiling for 32-bit, note that the size of int varies from 8 to 4 bytes
