#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
enum : size_t {
KB = 1024,
MB = 1024 * KB,
DFL_MAXSZ = 64 * MB,
DFL_STRIDE = 256,
NUM_ACCESS = 1ull << 24,
};
static inline uint64_t rdtsc() {
uint32_t eax, edx;
asm volatile("rdtsc" : "=a"(eax), "=d"(edx));
return ((uint64_t)edx << 32) | eax;
}
uint64_t run_one_walk(size_t size, size_t stride) {
// Check size is power of two.
assert((size & (size -1)) == 0);
assert((size / stride) <= NUM_ACCESS);
unsigned char *mem = (unsigned char *)malloc(size);
memset(mem, 0x55, size);
const uint64_t start = rdtsc();
for (size_t it = 0; it < NUM_ACCESS; it++) {
((volatile unsigned char *)mem)[(it * stride) & (size - 1)]++;
}
const uint64_t stop = rdtsc();
free(mem);
return stop - start;
}
int main(int argc, char *argv[]) {
size_t max_sz = DFL_MAXSZ;
size_t stride = DFL_STRIDE;
if (argc > 1) {
max_sz = strtoll(argv[1], 0, 10);
max_sz *= MB;
}
if (argc > 2) {
stride = strtoll(argv[2], 0, 10);
}
fprintf(stderr, "max_sz=%zuK stride=%zu access=%zu\n",
max_sz / KB, stride, NUM_ACCESS);
size_t size = 2048;
while (size <= max_sz) {
uint64_t cycles = 0;
for (size_t loop = 0; loop < 10; ++loop) {
cycles += run_one_walk(size, stride);
}
printf("%6zuK %f\n", size / KB, (double)cycles / NUM_ACCESS / 10.0);
size *= 2;
}
return 0;
}
