mmap_test

#include <sys/mman.h>
#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#define CLEAREOL "\e[0K"
#define CLOCK_START(a) double _clk_##a = now(); printf("%s... \n", #a)
#define CLOCK_STOP(a) printf(" ...%s: %.3fs\n", #a, now() - _clk_##a)

static double now() {
  struct timespec ts;
  clock_gettime(CLOCK_MONOTONIC, &ts);
  return ts.tv_sec + ts.tv_nsec * 1E-9;
}

int main() {
  setvbuf(stdout, NULL, _IONBF, 0);

  int fd = open("backing-file", O_RDWR | O_CREAT | O_TRUNC, 0666);
  if(fd == -1)
    err(1, "open");

  size_t len  = 200 * 1024 * 1024;
  size_t blen = 128 * 1024;

  CLOCK_START(write);
  char *buf = calloc(1, blen);
  for(size_t i = 0; i < len; i += blen) {
    printf("\rzeroing: %.1f MB" CLEAREOL, i * 1E-6);
    if(write(fd, buf, blen) != blen)
      err(1, "write\n");
  }
  free(buf);
  printf("\n");
  CLOCK_STOP(write);

  CLOCK_START(mmap);
  void *p = mmap(NULL, len, PROT_READ | PROT_WRITE,
     MAP_SHARED | MAP_NOSYNC | MAP_ALIGNED_SUPER, fd, 0);

  if(p == MAP_FAILED)
    err(1, "mmap");
  CLOCK_STOP(mmap);

  if(close(fd) == -1)
    err(1, "close");

  double start, stop, last;
  stop = start = now();
  int n = 0;
  do {
    memset(p, 0, len);
    last = stop; stop = now();

    double bw = 1E-6 * len / (stop - last);
    printf("\r%.1fs: memset #%d: %.1fMBps" CLEAREOL, stop - start, ++n, bw);
    if(bw < 500.0)
      printf(" - stalled\n");
  } while(stop - start < 100.0);
  printf("\noverall bandwidth: %.1fMBps\n", n * (double)len / (stop - start) * 1E-6);

  CLOCK_START(munmap);
  if(munmap(p, len) == -1)
    err(1, "munmap");
  CLOCK_STOP(munmap);

  printf("done\n");
  return 0;
}