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List:       busybox
Subject:    Question: different process's %cpu output via top from busybox and procps-ng
From:       Jie Zhang <wangyoucao577 () gmail ! com>
Date:       2016-12-16 3:03:55
Message-ID: CANzmr8hbiLBXmEV9dxVHJ3m_jOVc4JhA70smShNzN5ZDjm5k3Q () mail ! gmail ! com
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Hello everyone,

I have an `Embedded Linux(Kernel 2.6.37)` running on `ARM`. There's a
default `top` from `busybox 1.13.2`. And I build a `procps-ng 3.3.11` via
cross compile to run on this `Linux`. I found that the process's `%cpu` via
`top` output from `busybox` and `procps-ng` are different.

For example,  the `%cpu` of one process, `procps-ng top` display about 30%,
but `busybox top` display only about 10%. The total `%cpu` from `procps-ng
top` and `busybox top` are the same.
Then I read the calculation source code of `busybox` and `procps-ng`. I
found that they really have different calculation formula for one process's
`%cpu`.

<pre><code>
- busybox top:
    CPU% = s->pcpu/sum(s->pcpu) * busy_cpu_ticks/total_cpu_ticks
    (pcpu is delta of sys+user time between samples)

- procps-ng top:
    CPU% = s->pcpu/total_cpu_ticks
</code></pre>

Why the two projects choose different calculation formula? Do they designed
for different application case?


Looking forward to your reply.
Thanks very much!

[Attachment #5 (text/html)]

<div dir="ltr"><div class="gmail_default" \
style="font-family:verdana,sans-serif;font-size:small;color:#000000">Hello everyone,  \
<br></div><div class="gmail_quote"><div dir="ltr"><div><font color="#000000" \
face="verdana, sans-serif"><br></font></div><div><font color="#000000" face="verdana, \
sans-serif">I have an `Embedded Linux(Kernel 2.6.37)` running on `ARM`. There&#39;s a \
default `top` from `busybox 1.13.2`. And I build a `procps-ng 3.3.11` via cross \
compile to run on this `Linux`. I found that the process&#39;s `%cpu` via `top` \
output from `busybox` and `procps-ng` are different.     </font></div><div><font \
color="#000000" face="verdana, sans-serif"><br></font></div><div><font \
color="#000000" face="verdana, sans-serif">For example,   the `%cpu` of one process, \
`procps-ng top` display about 30%, but `busybox top` display only about 10%. The \
total `%cpu` from `procps-ng top` and `busybox top` are the same.     \
</font></div><div><font color="#000000" face="verdana, sans-serif">Then I read the \
calculation source code of `busybox` and `procps-ng`. I found that they really have \
different calculation formula for one process&#39;s `%cpu`.   </font></div><div><font \
color="#000000" face="verdana, sans-serif"><br></font></div><div><font \
color="#000000" face="verdana, \
sans-serif">&lt;pre&gt;&lt;code&gt;</font></div><div><font color="#000000" \
face="verdana, sans-serif">- busybox top:   </font></div><div><font color="#000000" \
face="verdana, sans-serif">      CPU% = s-&gt;pcpu/sum(s-&gt;pcpu) * \
busy_cpu_ticks/total_cpu_ticks     </font></div><div><font color="#000000" \
face="verdana, sans-serif">      (pcpu is delta of sys+user time between samples)   \
</font></div><div><font color="#000000" face="verdana, \
sans-serif"><br></font></div><div><font color="#000000" face="verdana, sans-serif">- \
procps-ng top:  </font></div><div><font color="#000000" face="verdana, sans-serif">   \
CPU% = s-&gt;pcpu/total_cpu_ticks   </font></div><div><font color="#000000" \
face="verdana, sans-serif">&lt;/code&gt;&lt;/pre&gt;</font></div><div><font \
color="#000000" face="verdana, sans-serif"><br></font></div><div><font \
color="#000000" face="verdana, sans-serif">Why the two projects choose different \
calculation formula? Do they designed for different application case?  \
</font></div><div><font color="#000000" face="verdana, \
sans-serif"><br></font></div><div><font color="#000000" face="verdana, \
sans-serif"><br></font></div><div><font color="#000000" face="verdana, \
sans-serif">Looking forward to your reply.  </font></div><div><font color="#000000" \
face="verdana, sans-serif">Thanks very much!</font></div></div> </div><br></div>



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