[collectd] CPU Graphs seems out of sync

Florian Forster octo at verplant.org
Tue Jun 3 19:47:21 CEST 2008

Hi Shibashish,

On Tue, Jun 03, 2008 at 12:49:29PM +0530, Shibashish wrote:
> In the CPU graphs, in some (2) of the hosts, the vertical axis starts as 0,
> 200, 400, 600, 800. And one of the host shows as 0, 0.5k, 1.0k. Why is this
> so ? How can percent go beyond 100 ? Or is the plotting showing correct data
> ? Is there a way to correct this ?

the CPU plugin collects ``jiffies'' or ``system timer interrupts''.
Typical values for a Linux kernel are 1/100s and 1/250s, but you can set
this to 1/1000s for (near) realtime systems, too.

So there are 100, 250, or 1000 jiffies in one second. So given the
values I'd guess that the kernel of your distribution is built with the
HZ variable set to 1000 at build time. Unfortunatly I don't know how you
can double check this, but I'm sure Google will be able to assist you ;)

You can convert this number to a percentage, which is easier to compare
between machines, using RRDTool's ``RPN'' functionality. You'd need to
do something along these lines:
Then graph `user_pct', `syst_pct', and `idle_pct'.

Florian octo Forster
Hacker in training
GnuPG: 0x91523C3D
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