On Mon, 9 Jun 2008, Nick Davey wrote:
I've deployed rancid on a fairly large metro network, and am seeing some
pretty high CPU averages. When RANCID runs the CPU's on a large number of
our boxes spike to about 95% for several seconds. Although they have never
hit 100%, or caused any issues (dropped OSPF hello's, stp bpdu's) I'm
concerned that this could happen under the right combination of events this
could result is dropped OSPF neighbor adjacency's or other badness.
I've tried to replicate the high CPU issue by pasting the commands in
manually however I haven't come anywhere close to the 95% I'm seeing when
RANCID runs them. I'm assuming this is just the frequency at which the
commands are run. Does anyone have any experience with this or any insight
they can provide?
Keep in mind that interactive logins and the processes that are needed to
service those sessions do carry a CPU cycle penalty. Also, traffic _to_ a
device, as opposed to through it, is normally process switched, so that's
another CPU hit right there. How quickly the commands are run can
certainly play into how much the CPU gets beaten up.
Also how are you looking at the CPU spikes? If you're doing something
like a "show proc cpu hist", that usually does a pretty good job of
showing you some of the transient spikes that the 'legacy' CPU utilization
OID can miss. From what I recall, the 5 second CPU utilization OID in the
CISCO-PROCESS-MIB gives results that more closely resemble the command
above.
jms
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