clock_gettime比gettimeofday更加精确
简单做了一下测试
先用clock_gettime做一下测试
test.c
#include<time.h> #include<stdio.h>
#define MILLION 1000000
int main(void) { struct timespec tpstart; struct timespec tpend; long timedif;
clock_gettime(CLOCK_MONOTONIC, &tpstart); clock_gettime(CLOCK_MONOTONIC, &tpend); timedif = MILLION*(tpend.tv_sec-tpstart.tv_sec)+(tpend.tv_nsec-tpstart.tv_nsec)/1000; fprintf(stdout, "it took %ld microseconds/n", timedif);
return 0; }
|
在linux 2.6内核下面
gcc -o test test.c -lrt
./test
得到结果:
it took 2 microseconds
现在用gettimeofday来做一下测试
#include<time.h> #include<stdio.h>
#define MILLION 1000000
int main(void) { struct timespec tpstart; struct timespec tpend; long timedif;
gettimeofday(&tpstart, NULL); gettimeofday(&tpend, NULL); timedif = MILLION*(tpend.tv_sec-tpstart.tv_sec)+(tpend.tv_nsec-tpstart.tv_nsec)/1000; fprintf(stdout, "it took %ld microseconds/n", timedif);
return 0; }
|
gcc -o test test.c
./test
得到结果:
it took 0 microseconds
AIX下面也得到同样的结果
而且可以通过clock_gettime这个函数测试出64位程序要比32为程序运行快
在AIX P570,16个CPU 15.5G内存机器上测试了一把
用64位模式得到的结果是 0 microseconds
用32位模式得到的结果是 1 microsecond