mispredict_penalty.c

#define NOP ({ int x; asm("nop" : "=r"(x)); asm("" : : "r"(x)); })

NOINLINE
double calc_mispredict_penalty(void) {
	i64 n = 1ull << 28;

	u64 rnglen = (n + 63) / 64;
	u64 *rng = malloc(rnglen * sizeof(u64));
	for (u64 i = 0; i < rnglen; i++)
		rng[i] = random_u64();
	u64 *next = rng;

	i64 i = n;
	start_timer();
	do {
		u64 bits = *next++;
		#pragma unroll(64)
		for (int k = 0; k < 64; k++) {
			if (bits & (1ull << k)) {
				RW(i);
				NOP;
			}
		}
		RW(i);
		i -= 64;
	} while (i >= 0);
	double secs = stop_timer();
	double cycles = secs * cpufreq;
	double penalty = 2.0 * cycles / n;
	free(rng);
	return penalty;
}