Test performance of stat vs open on non-existent files

syscall_perf.cpp

#include <stdio.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <assert.h>

#include <chrono>
#include <string>

int main (int argc, const char** argv) {
  if (argc != 2) {
    fprintf(stderr, "Usage: %s [stat|open]\n", argv[0]);
    return 1;
  }
  std::string syscall_to_test = argv[1];
  if (syscall_to_test != "stat" && syscall_to_test != "open") {
    fprintf(stderr, "Usage: %s [stat|open]\n", argv[0]);
    return 1;
  }

  printf("Calling %s() 10,000 times on non-existent files\n", syscall_to_test.c_str());

  auto begin = std::chrono::high_resolution_clock::now();

  for (int i = 0; i < 100; i++){
    for (int j = 0; j < 100; j++){
      std::string path = "/usr/local/lib/file_does_not_exist_" + std::to_string(j);
      if (syscall_to_test == "stat") {
        struct stat file_info;
        int error;

        error = stat(path.c_str(), &file_info);
        assert (error != 0);
      }
      else {
        int fd;
        assert(open(path.c_str(), O_RDONLY) == -1);
      }
    }
  }

  auto end = std::chrono::high_resolution_clock::now();
  auto elapsed = std::chrono::duration_cast<std::chrono::nanoseconds>(end - begin);

  printf("Time measured: %.6f seconds.\n", elapsed.count() * 1e-9);
  printf("%.2f usec per call.\n", elapsed.count() / 10000 * 1e-3);

  return 0;
}