[c-nsp] High CPU load from loose TE tunnels

[Rodney Dunn]

What code?

The CEF scanner is gone in later code. We moved it to an entirely event
driven architecture.

A sh ip cef events might help explain what the scanner is trying to
do. It's a bit more complicated with MPLS enabled because some of
the MPLS code can make callbacks to the CEF scanner even though it's
not CEF at all.

debug mpls lfib cef|enc|adj might tell the answer if that's what it
is.

Rodney

 
On Tue, Jan 23, 2007 at 05:01:53PM +0000, Anton Smith wrote:
> Hi all,
> 
> I am having a problem with high CPU load on a 7600 because of a downed 
> TE tunnel that is configured to use a path that starts with a loose hop, 
> followed by strict hops. The tunnel is down because one of the strict 
> hops is not reachable (physical link down). The tunnel and path config 
> are as follows:
> 
> interface Tunnel111
>   description Tunnel111
>   ip unnumbered Loopback1
>   tunnel destination x.x.x.4
>   tunnel mode mpls traffic-eng
>   tunnel mpls traffic-eng autoroute announce
>   tunnel mpls traffic-eng priority 2 2
>   tunnel mpls traffic-eng path-option 1 explicit name path1
>   tunnel mpls traffic-eng load-share 155
> 
> ip explicit-path name path1 enable
>   index 2 next-address loose x.x.x.1
>   next-address x.x.x.2
>   next-address x.x.x.3
>   next-address x.x.x.4
> 
> 
> Other tunnels that are configured with paths that are very similar (and 
> are fully up) do not cause this kind of CPU load. But when they go down, 
> they also create the same kind of load.
> 
> The CPU histogram looks as follows:
> 
>        44444     44444     44444    444444444455555     44444
>       233333     66666     7777788886666655555444441111166666
> 100
>   90
>   80
>   70
>   60
>   50             *****     *****    ***************     *****
>   40   *****     *****     *****    ***************     *****
>   30   *****     *****     *****    ***************     *****
>   20   *****     *****     *****    ***************     *****
>   10   *****     *****     ************************     *****
>      0....5....1....1....2....2....3....3....4....4....5....5....
>                0    5    0    5    0    5    0    5    0    5
> 
>                 CPU% per second (last 60 seconds)
> 
> And the process that seems to be causing the load is CEF scanner:
> 
> CPU utilization for five seconds: 44%/0%; one minute: 29%; five minutes: 18%
>   PID Runtime(ms)   Invoked      uSecs   5Sec   1Min   5Min TTY Process
>   114    43044320   1823442      23606 37.11% 21.28% 11.57%   0 CEF 
> Scanner
> ....
> 
> If I admin shut the tunnel interface in question, the CPU load drops 
> back to near zero.
> 
> I notice that when I run show mpls traffic-eng tunnels summary, the 
> activations and deactivations numbers increment steadily every few 
> seconds, as though the box is continually trying to bring up the tunnel 
> (more often than it should?):
> 
> R1#show mpls traffic-eng tunnels summary
> Signalling Summary:
>      LSP Tunnels Process:            running
>      Passive LSP Listener:           running
>      RSVP Process:                   running
>      Forwarding:                     enabled
>      Head: 15 interfaces, 13 active signalling attempts, 13 established
>            23356 activations, 23343 deactivations
>      Midpoints: 0, Tails: 13
>      Periodic reoptimization:        every 300 seconds, next in 213 seconds
>      Periodic FRR Promotion:         Not Running
>      Periodic auto-bw collection:    every 300 seconds, next in 269 seconds
> 
> I have another router (the tail), which has return tunnels built (also 
> using a combination of loose and strict hops). This router also has a 
> downed tunnel interface (for the same reason that the first router does 
> - i.e. a downed physical link on a strict hop), but it does not exhibit 
> high CPU load nor does it seem to be periodic. In addition, the 
> 'activations' and 'deactivations' counters do not increment. However, 
> this other router is a 7301. The tunnels are not administratively shut 
> on the 7301.
> 
> Does anybody have any ideas? How frequently does a 7600 attempt to bring 
> up a tunnel interface? I imagine that the CPU load is coming from the 
> CSPF calculation being run every few seconds in an attempt to find a 
> path to the first (loose) hop. Is it possible to change this frequency? 
> (I have tried changing the reoptimisation timers but I do not believe 
> this is the problem, since they are by default 300 seconds - and I see 
> high CPU load every few seconds).
> 
> Any help much appreciated :).
> 
> Regards,
> Anton
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