snmp cpu

[Dan Nelson]

In the last episode (Nov 30):
> Hi,
> reading this:
> http://old.nabble.com/Measuring-CPU-usage-via-SNMP-td23392403.html
> 
> > So fetching the matching ssCpuRaw* oids and totaling them up should
> > always equal 100% cpu.
> 
> but when I fetch cpurawidle it is about 100, system 25
> totalling give me 125. What wrong I do?

Hey! I recognize that post :)  Note that ssCpuRawSystem is a synthetic value
that net-snmp generates by adding ssCpuRawKernel and ssCpuRawInterrupt.  If
you are doing the totalling yourself, you should ignore it, or you'll be
counting kernel time twice.

In case anyone else reading is unclear:

Totalling the raw values always gives 100% cpu, but the units aren't
percent; they're ticks.  You may get a different total on different
machines, depending on Hz and the number of CPUs.  If you want to graph the
values as percentages, you'll need to record the previous values for each
variable, then sum the differences to get the total number of ticks for your
sampling period.  Then divide each variable's difference by that total to
get a percentage.

Raw values on my machine using a ~ 5-second sampling period:

User      Nice      Idle        Kernel     Interrupt
14993233  67689938  1943767096  171721693  11277468
14993237  67690250  1943768892  171722224  11277487
14993246  67690357  1943770991  171722649  11277495

Deltas:
4         312       1796        531        19    Total: 2662
9         107       2099        425        8     Total: 2648

Percent:

0.2       11.7      67.5        19.9       0.7
0.3       4.0       79.3        16.0       0.3

-- 
	Dan Nelson
	dnelson at allantgroup.com