cpu时钟预取实例代码分享
测试下预取的效果，利用cpu始终查看效果。根据实验发现，预取地址在地址使用之前的十行左右代码处效果比较好！
#include <stdio.h>
#define max_len 1000000
static inline void prefetchnta(void *addr) //预取部分
{
__asm__("movl %0, %%eax"::"a"(addr));
__asm__(".byte 0x0f, 0x18, 0x00");
}
inline unsigned long long getcputickcount()
{
unsigned long high32 = 0;
unsigned long low32 = 0;
__asm__("rdtsc" : "=a"(low32), "=d"(high32));
unsigned long long counter = high32;
counter = (counter<<32) + low32;
return counter;
}
int main(int argc, char* argv[])
{
long long start, end;
long long array[max_len];
int i;
for(i = 0; i < max_len； i++) //让cache失效
array[i]++;
start = getcputickcount();
array[0]++;
end = getcputickcount();
printf("don't use prefetch time:%ld\n", end - start);
for(i = 0; i < max_len； i++)
array[i]++;
prefetchnta(array);
start = getcputickcount();
array[0]++;
end = getcputickcount();
printf("use prefetch time:%ld\n", end - start);
return 0;
}