high switching processor utilization !

[kthned]

Hi

I am seeing a strange situation on my 6500 switch which I am not able to understand and hence asking :).

By having snmp walk on '1.3.6.1.4.1.9.9.109.1.1.1.1.3' (== cpmCPUTotal5sec), I came to know that there are two processor and the cpu util for switching processor is gone to 88 % and some time creeps to 99 %.

snmpwalk -v2c -c "removes"  sw6500 '1.3.6.1.4.1.9.9.109.1.1.1.1.3'

SNMPv2-SMI::enterprises.9.9.109.1.1.1.1.3.1 = Gauge32: 12 (--- this is for CPU of Router Processor )

SNMPv2-SMI::enterprises.9.9.109.1.1.1.1.3.3 = Gauge32: 99 (--- this is for CPU of Switching Processor )

but when I do sh process cpu on the console, all looks normal as it shows cpu utilization of RP.

Can some one help me, why the value is so high on the switching processor ?

Thanks is advance

//umair

[Arumugam Muthaiah]

Hi Umair,

The SNMP Object 1.3.6.1.4.1.9.9.109.1.1.1.1.3 cpmCPUTotal5sec indicates that the overall CPU busy percentage in the last 5 second period.

When you execute the show process cpu will show you the CPU utilization on Router process (RP) only. But you are seeing the spike on Switch process (SP)

There are two types of CPU’s.

1. One is used for layer 2 operations and is commonly referred as the SP (Switch Processor) CPU. 
   
2. The other CPU is used for layer3/4 operations and it commonly referred to as the RP(Route Processor) CPU. Both of these processors are located on the MSFC3 complex, each with a 1 gig in-band channel to the supervisor
   

High CPU on the SP (Switch processor):
High CPU on the SP is much less common than high CPU on the RP.  The reasons for high CPU on the SP are typically related to layer 2 operations, such a spanning-tree (processing of BPDU's) or processing IGMP snooping / IGMP queries / membership reports as well as LACP/PAGP.

You can view the CPU utilization using the following command:

SP CPU Util:
Switch# remote command switch show process cpu

OR

Switch# remote login switch
Switch-sp#show process cpu

There are two type of CPU utilization within IOS, interrupt and process.

CPU utilization caused by a process

1. Processes switched traffic. This is traffic that is hitting a specific process in order to be forwarded OR processed by the CPU.  An example of each would traffic being forwarded via the "IP Input" process OR control-plane traffic hitting the "PIM process".
   
2. A process trying to clean up tables/previous actions performed.  This can be seen in process such a "CEF Scanner" or "BGP Scanner", which are used to clean/update the CEF and BGP tables.
   

Interrupt based CPU utilization:
CPU caused by an interrupt is always traffic based. Interrupt switched traffic, is traffic that does not match a specific process, but still needs to be forwarded.

Determining the type of CPU utilization:

Process and Interrupt CPU utilization are listed within the "show process cpu" command. This is broken down below on how to determine what percentage of the CPU utilization is due to interrupt traffic or processed switched traffic:

6500-3#sh proc cpu

CPU utilization for five seconds: X%/Y%; one minute: 0%; five minutes: 0%

X indicates the percentage of total CPU utilization

Y indicates Percentage of the CPU that is caused by Interrupts.

Percentage of process CPU util. = Total CPU - Interrupt CPU util.

Need to troubleshoot this issue according to the type of the CPU Utilization. Please see the below doc which helps to understand this CPU utilization.

Refer:

https://supportforums.cisco.com/docs/DOC-15602

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

Regards,

Aru

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