CPU Wakeup Speed Tester

CPUWakeupSpeedTester.cpp

#include <string.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

extern "C" size_t test(size_t amt);

template <size_t Len, size_t Iters>
struct Tester {
	size_t data[Iters][Len];

	void run(useconds_t sleep_us, int sleep_count, size_t iterlen) {
		for (auto& iter : data) {
			for (int i = 0; i < sleep_count; i++)
				usleep(sleep_us);
			for (size_t i = 0; i < Len; i++) {
				auto& pt = iter[i];
				pt = test(iterlen);
			}
		}
	}

	void results() {
		size_t min = SIZE_MAX;
		static constexpr int HIST_MAX = 8;
		static constexpr int HIST_RES = 4; // Bucket size: Min/HIST_RES
		int histograms[Len][HIST_MAX] = {};

		for (const auto& iter : data) {
			for (auto pt : iter) {
				if (min > pt) { min = pt; }
			}
		}

		for (const auto& iter : data) {
			for (size_t i = 0; i < Len; i++) {
				auto pt = iter[i];
				auto& hist = histograms[i];
				auto quartile = (pt - min) / (min / HIST_RES);
				if (quartile < HIST_MAX) {
					hist[quartile]++;
				}
			}
		}

		printf("%8zu Baseline\n", min);
		int digits[HIST_MAX] = {};
		for (const auto& hist : histograms) {
			for (int i = 0; i < HIST_MAX; i++) {
				int v = hist[i];
				int digitcount = 1;
				while (v >= 10) {
					digitcount++;
					v /= 10;
				}
				if (digits[i] < digitcount) { digits[i] = digitcount; }
			}
		}
		for (const auto& hist : histograms) {
			printf("%2zd: ", (&hist - histograms));
			for (int i = 0; i < HIST_MAX; i++) {
				char fmt[10];
				sprintf(fmt, "%%%dd ", digits[i]);
				printf(fmt, hist[i]);
			}
			printf("\n");
		}
	}
};

int main(int argc, const char * argv[]) {
	Tester<32, 1000> tester;
	tester.run(4000, 1, 100000);
	tester.results();
	tester.run(1000, 1, 100000);
	tester.results();
	return 0;
}

CPUWakeupSpeedTester.s

.intel_syntax
.globl _test
_test:
	rdtsc
	shl rdx, 32
	or rax, rdx
	mov rcx, rax
loop:
	add rdx, rdx
	add rdx, rdx
	add rdx, rdx
	add rdx, rdx
	dec rdi
	jne loop

	rdtsc
	shl rdx, 32
	or rax, rdx
	sub rax, rcx
	ret