<div dir="ltr">in kernel you should use this func:<div><div>static unsigned long usec(void)</div><div>{</div><div>        struct timeval tv;</div><div>        do_gettimeofday(&tv);</div><div>        return (unsigned long)tv.tv_sec * 1000000 + tv.tv_usec;</div><div>}</div></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">2018-07-09 15:54 GMT+08:00 袁建鹏 <span dir="ltr"><<a href="mailto:yuanjp@hust.edu.cn" target="_blank">yuanjp@hust.edu.cn</a>></span>:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class=""><span style="font-size:14px;white-space:normal">can you show all code kernel and userspace ?</span>
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        Kernel compile options are optimized, very different from userspace.
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        you can use the same object (memcpy.o) to link userspace program and kernel module.
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        -----原始邮件-----<br>
<b>发件人:</b><span id="m_2272497773717310661rc_from">"bing zhu" <<a href="mailto:zhubohong12@gmail.com" target="_blank">zhubohong12@gmail.com</a>></span><br>
<b>发送时间:</b><span id="m_2272497773717310661rc_senttime">2018-07-08 22:03:48 (星期日)</span><br>
<b>收件人:</b> "Valdis Kletnieks" <<a href="mailto:valdis.kletnieks@vt.edu" target="_blank">valdis.kletnieks@vt.edu</a>><br>
<b>抄送:</b> <a href="mailto:kernelnewbies@kernelnewbies.org" target="_blank">kernelnewbies@kernelnewbies.<wbr>org</a><br>
<b>主题:</b> Re: Question about memcpy<br>
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                        void *p = malloc(4096 * max);
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                        start = usec();
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                        for (i = 0; i < max; i++) {
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                        memcpy(p + i * 4096, page, 4096);
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                        }
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                        end = usec();
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                        printf("%s : %d time use %lu us \n", __func__, max,end - start）;
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                        static unsigned long usec(void)
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                        {
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                                struct timeval tv;
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                                gettimeofday(&tv, 0);
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                                return (unsigned long)tv.tv_sec * 1000000 + tv.tv_usec;
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                        }
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                        I'm don't think it's really precise but i did notice a difference ,
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                        2018-07-08 2:44 GMT+08:00 <span dir="ltr"><<a href="mailto:valdis.kletnieks@vt.edu" target="_blank">valdis.kletnieks@vt.edu</a>></span>:<br>
                        <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
                                <span>On Sat, 07 Jul 2018 19:36:47 +0800, bing zhu said:<br>
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> and in user space i do the same thing,I noticed that kernel is faster than<br>
> user ,<br>
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</span>How did you measure the times? Doing this right is actually harder than it looks...<br>
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