High CPU utilization

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Nov 4th, 2009
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Hello Pros,


In my 3845 , i am getting high cpu usage but i am not able to find out for what reason it is so much utilized.


Router1#sh processes cpu sorted

CPU utilization for five seconds: 64%/61%; one minute: 63%; five minutes: 62%


Not a single process is taking more than 0.5 % of utilization.


Is there is any way to find the exact problem?




Many Thanks

Prasad


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Overall Rating: 3.5 (2 ratings)
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slmansfield Wed, 11/04/2009 - 08:42
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Joseph W. Doherty Wed, 11/04/2009 - 09:41
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"CPU utilization for five seconds: 64%/61%; one minute: 63%; five minutes: 62% "


The bolded value indicates most of your CPU is "interrupt" CPU; normally traffic forwarding CPU. What's the aggregate bandwidth passing through the router while the CPU is like this?

Manish Prasad Wed, 11/04/2009 - 12:39
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Its a DS3 link.


Router1# sh interfaces ATM3/0 | inc rate

Queueing strategy: Per VC Queueing

5 minute input rate 18606000 bits/sec, 6150 packets/sec

5 minute output rate 27905000 bits/sec, 6341 packets/sec



Thanks

Prasad

Joseph W. Doherty Wed, 11/04/2009 - 13:01
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For a 3845, I would have expected the CPU usage to be somewhat lower for about 46 Mbps, but perhaps your configuration, if doing more than just routing packets (e.g. ACLs, etc.) is adding to the CPU load. Reviewing the references that Susan provided, or like ones found searching Cisco's site, might help. Unfortunately, as far as I know, there's no easy way to "see" what portion or kind of interrupt processing is consuming CPU to help narrow the issue.


Do understand, though, that software based routers do load up the CPU as traffic increases. When the traffic gets to the point where CPU load is excessive, sometimes the only cure is a faster or multiple routers.


Don't know if that's the case in your instance. Again, I would have expected a lower CPU for 46 Mbps on a 3845.


BTW, the 46 Mbps represents all the traffic transiting the router? I.e. the router also isn't supporting any other LAN routing?

Manish Prasad Wed, 11/04/2009 - 13:36
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Thank You for all your support.


It is resolved now after using the command "max-reserved-bandwidth %".



Thanks

Prasad

Joseph W. Doherty Wed, 11/04/2009 - 13:44
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That's very interesting! So, just want to confirm, changing/using max-reserved-bandwidth (on your ATM interface?) changed/reduced CPU utilization for the same traffic load utilization?

Manish Prasad Wed, 11/04/2009 - 15:10
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There was some mismatch between COS(D2 profile) and bandwidth percentage due to this the interface utilization was high and also by default cisco ISO allocate 75 percent of bandwith only.So we changed it to 90 percent which decrease down the CPU utilization to 38 %.

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