callbench: clock timing

callbench.c

#include <fcntl.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/auxv.h>
#include <sys/time.h>
#include <syscall.h>
#include <time.h>
#include <unistd.h>

extern void vdso_init_from_sysinfo_ehdr(uintptr_t base);
extern void *vdso_sym(const char *version, const char *name);

int main(int argc, char **argv) {
  int m = 0, i, n = 1000000;
  int (*cgt)(clockid_t, struct timespec *);
  void *e;
  struct timespec ts;

  if (argc > 2)
    n = atoi(argv[2]);
  if (argc > 1)
    m = atoi(argv[1]);
  switch (m) {
  case 0:
    for (i = 0; i < n; i++)
      clock_gettime(CLOCK_MONOTONIC, &ts);
    break;
  case 1:
    for (i = 0; i < n; i++)
      syscall(SYS_clock_gettime, CLOCK_MONOTONIC, &ts);
    break;
  case 2:
    vdso_init_from_sysinfo_ehdr(getauxval(AT_SYSINFO_EHDR));
    cgt = (int (*)(clockid_t, struct timespec*)) vdso_sym("LINUX_2.6", "clock_gettime");
    if (cgt == NULL)
      exit(1);
    for (i = 0; i < n; i++)
      cgt(CLOCK_MONOTONIC, &ts);
    break;
  case 10:
    e = sbrk(0);
    for (i = 0; i < n; i++)
      brk(e);
    break;
  case 11:
    for (i = 0; i < n; i++)
      fcntl(-1, 0, 0);
    break;
  default:
    fprintf(stderr, "Usage: %s cmd cycles\n"
      "0=clock_gettime, 1=SYS_clock_gettime, 2=vDSO, 10=brk, 11=fcntl\n",
      argv[0]);
    exit(1);
    break;
  }
}

Makefile

callbench: callbench.o parse_vdso.o
	musl-gcc -o $@ $? -lrt -static
	sstrip $@

%.o: %.c
	musl-gcc -c $< -o $@

clean:
	rm *.o callbench

parse_vdso.c

// From Documentation/vDSO/parse_vdso.c in linux.git