Test speed of memory access across different pages

mem_speed_test.cpp

#include <cstdio>
#include <vector>
#include <chrono>
#include <thread>

static constexpr int test_size = 100000;
static constexpr int page_size = 4096;

static int data[test_size * page_size];
static int index[test_size];

static double run(bool warm_up, int n)
{
	for (int i = 0; i < test_size; ++i)
	{
		index[i] = (i * page_size + (n % 100)) % (page_size * n);
	}

	if (warm_up)
	{
		for (int i = 0; i < test_size; ++i)
		{
			data[index[i]] = 1;
		}
	}

	auto start = std::chrono::high_resolution_clock::now();
	for (int i = 0; i < test_size; ++i)
	{
		data[index[i] + 1] = 2;
	}
	auto end = std::chrono::high_resolution_clock::now();
	return (end - start).count() / 1000000.0;
}

static void flush_cache()
{
	std::this_thread::yield();
	for (int i = 0; i < test_size; ++i)
	{
		data[i * page_size] = 0;
	}
}

int main(int argc, const char* argv[])
{
	std::vector<int> s;
	for (int i = 1; i < test_size; i *= 2)
	{
		s.push_back(i);
	}
	s.push_back(test_size);

	std::printf("Warm up.\n");
	for (std::size_t i = 0; i < s.size(); ++i)
	{
		std::printf("%d:\t%f\n", s[i], run(true, s[i]));
		flush_cache();
	}

	std::printf("\nNo warm up.\n");
	for (std::size_t i = 0; i < s.size(); ++i)
	{
		std::printf("%d:\t%f\n", s[i], run(false, s[i]));
		flush_cache();
	}

	std::getchar();

	return 0;
}