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Debugging High CPU in WAAS Deployment

2007
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Introduction

High CPU is one of the most common symptom observed by users when troubleshooting some issue with WAAS. High CPU in WAAS could be because of some geniune reason and as such this should not cause any problem. If high CPU stays for a long period of time, more investigation is required to get to the root cause of the issue.

 

Troubleshooting High CPU

Check the following for understanding the cause of high CPU

 

Determine the process causing High CPU

Use command such as: show process cpu | ex 0.0 to pick on process that uses any CPU time. Follow the link for more info on this.

 

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00804916e0.shtml

 

Determine Traffic that is Punted

This will list packets that are software switched instead of hardware. Follow the link for more info on this.

 

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00804916e0.shtml#utilities

 

Determine if CPU Utilization is due to Interrupts

This will show if any CPU Interrupts are responsible for high CPU. Follow the link for more info.

 

http://www.cisco.com/en/US/products/hw/routers/ps133/products_tech_note09186a00800a70f2.shtml#high_cpu

 

Determine if CPU Utilization is due to ACLs

This will show if any ACL is using too much processing leading to high CPU. Follow the link for more info.

 

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00804916e0.shtml#oal

 

Profiling

Profiling is used for determining what is causing the issue. Here is an example from a profiling used for determining high cpu cause (from a BGP based Example):

 

a) Run a "show region". Take special note of the "Start" address for the "main:text" region. For example..

 

Test#show region

 

Region Manager:

 

Start         End     Size(b)  Class  Media  Name

 

0x60008BD8  0x6191C1F4    26293789  IText  R/O    main:text

++++

 

In this command output the "start" is 60008BD8  and the "end" is 6191C1F4.

 

b) Next turn on "profile" by configuring the following: profile 60008BD8 6191C1F4 10

 

In this case 60008BD8 would be the start of main:text address and 6191C1F4 would be the end of main:text. The 10 represents the rate of granularity that the profiling needs to be configured at. You would run the above command for about 3 minutes.

 

c) Next start the "profile" by configuring "profile start" and let this run for 10 mins the "profile stop"

 

d) Turn off the "more" page scrolling feature as you would be collecting large info by the following config: "term len 0"

 

e) Collect the "CPU" profile info by configuring:

 

show profile ter

show profile detail

 

Note: The above info would be lengthy and you would want to set the logging.

 

f) Finally enter the following commands:

 

clear profile

unprofile   all

 

Check the output data to understand what is causing the issue.

 

Related Information

Cisco WAAS Troubleshooting Guide for Release 4.1.3 and Later

Comments
Participant

Maybee you should point out the this article is related to High CPU in surrounding Network Equipment (switches and routers) and not directly related to WAAS.

WCCP (or even PBR) migth cause CPU issues in routers/switches running WCCP/PBR.

Best regards

Finn

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