[collectd] Questions about coding standards & writing plugins

[Richard W.M. Jones]

Florian Forster wrote:
> The CPU plugin, at least under Linux, reports ``Jiffies'', i. e.
> timeticks that are defined by the `HZ' value in the kernel, usually
> either 1/100th, 1/250th or 1/1000th of a second. So the values should be
> seen in relation to each other anyways, so if for example `system' is
> 25, `user' is 150 and `idle' is 75, you'd get 10%, 60% and 30%
> respectively.

So the nanosecond figure comes from the Xen hypervisor which is a layer 
sitting under the Linux kernel (or in fact kernels because usually you 
are running a "dom0" management domain and a number of "domU" guests). 
I will ask our hypervisor experts here how accurate the number really 
is.  Then I can decide whether to scale it to jiffies or just leave it.

> As for the maximum value: This value is checked after the counter value
> has been converted to a rate. So the maximum value should be 10^9 in
> your case (possibly plus 5% so account for measurement errors), because
> the (theoretical) maximum is 10^9 nanoseconds per second.

Oh I see, I didn't realise that :-)

Rich.

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