Question about memcpy

[bing zhu]

in kernel you should use this func:
static unsigned long usec(void)
{
        struct timeval tv;
        do_gettimeofday(&tv);
        return (unsigned long)tv.tv_sec * 1000000 + tv.tv_usec;
}


2018-07-09 15:54 GMT+08:00 袁建鹏 <yuanjp at hust.edu.cn>:

> can you show all code kernel and userspace ?
>
> Kernel compile options are optimized, very different from userspace.
>
> you can use the same object (memcpy.o) to link userspace program and
> kernel module.
>
> -----原始邮件-----
> *发件人:*"bing zhu" <zhubohong12 at gmail.com>
> *发送时间:*2018-07-08 22:03:48 (星期日)
> *收件人:* "Valdis Kletnieks" <valdis.kletnieks at vt.edu>
> *抄送:* kernelnewbies at kernelnewbies.org
> *主题:* Re: Question about memcpy
>
> void *p = malloc(4096 * max);
> start = usec();
> for (i = 0; i < max; i++) {
> memcpy(p + i * 4096, page, 4096);
> }
> end = usec();
> printf("%s : %d time use %lu us \n", __func__, max,end - start）;
>
> static unsigned long usec(void)
> {
>         struct timeval tv;
>         gettimeofday(&tv, 0);
>         return (unsigned long)tv.tv_sec * 1000000 + tv.tv_usec;
> }
>
>
> I'm don't think it's really precise but i did notice a difference ,
>
> 2018-07-08 2:44 GMT+08:00 <valdis.kletnieks at vt.edu>:
>
>> On Sat, 07 Jul 2018 19:36:47 +0800, bing zhu said:
>>
>> > and in user space i do the same thing,I noticed that kernel is faster
>> than
>> > user ,
>>
>> How did you measure the times? Doing this right is actually harder than
>> it looks...
>>
>
>
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