How much does a simple syscall (such as `getpid`) cost in CPU cycle?

bench.c

#include <unistd.h>
#include <stdint.h>
#include <stdio.h>

uint64_t rdtsc();

#ifdef __i386
__inline__ uint64_t rdtsc() {
  uint64_t x;
  __asm__ volatile ("rdtsc" : "=A" (x));
  return x;
}
#elif defined __amd64
__inline__ uint64_t rdtsc() {
  uint64_t a, d;
  __asm__ volatile ("rdtsc" : "=a" (a), "=d" (d));
  return (uint64_t)(d<<32) | a;
}
#endif


int main()
{
  	uint64_t begin = rdtsc();
		getpid();
		uint64_t end = rdtsc();
		printf("begin: %llu end: %llu duration: %llu\n", begin, end, end-begin);
		return 0;
}