l1_size.cpp

#include <chrono>
#include <cstdlib>
#include <iostream>

constexpr auto MAX = 1 << 24;

char accessMemory(char *buf, size_t n) { return buf[0] ^ buf[n - 1]; }

char *align(char *buf, size_t &size, size_t alignment) {
  while ((uint64_t)buf & (alignment - 1)) {
    if (!size) {
      throw std::exception();
    }
    ++buf;
    --size;
  }
  return buf;
}

int main() {
  uint64_t prevTime = 0;
  for (size_t n = 1; n <= MAX; n *= 2) {
    size_t size = 2 * n;
    char *buful = (char *)std::calloc(sizeof(char), size);
    char *buf = align(buful, size, n);
    char x = buf[0]; // warm l1 cache
    auto now = std::chrono::steady_clock::now();
    accessMemory(buf, size);
    int elapsed = (std::chrono::steady_clock::now() - now).count();
    std::free(buful);
    /*
    if (prevTime > 0 && elapsed / prevTime > 7) {
      std::cout << n << std::endl;
      return 0;
    }
    */
    std::cout << "n: " << n << " elapsed: " << elapsed << std::endl;
    prevTime = elapsed;
  }
}