1 // Author: Suleiman Souhlal (suleiman (at) google.com) 2 3 #include <stdio.h> 4 #include <err.h> 5 #include <stdint.h> 6 #include <sys/types.h> 7 #include <sys/stat.h> 8 #include <sys/mman.h> 9 #include <fcntl.h> 10 11 #define O_NOATIME 01000000 12 13 inline uint64_t 14 rdtsc(void) 15 { 16 int64_t tsc; 17 18 __asm __volatile("rdtsc" : "=A" (tsc)); 19 return (tsc); 20 } 21 22 int 23 main(int argc, char **argv) 24 { 25 struct stat st; 26 uint64_t e, s, t; 27 char *p, q; 28 long i; 29 int fd; 30 31 if (argc < 2) { 32 printf("Usage: %s <file>\n", argv[0]); 33 return (1); 34 } 35 36 if ((fd = open(argv[1], O_RDWR | O_NOATIME)) < 0) 37 err(1, "open"); 38 39 if (fstat(fd, &st) < 0) 40 err(1, "fstat"); 41 42 p = mmap(NULL, st.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0); 43 44 t = 0; 45 for (i = 0; i < 1000; i++) { 46 *p = 0; 47 msync(p, 4096, MS_SYNC); 48 s = rdtsc(); 49 *p = 0; 50 __asm __volatile(""::: "memory"); 51 e = rdtsc(); 52 if (argc > 2) 53 printf("%d: %lld cycles %jd %jd\n", i, e - s, (intmax_t)s, (intmax_t)e); 54 t += e - s; 55 } 56 57 printf("average time: %lld cycles\n", t / 1000); 58 59 return (0); 60 } 61
