Tuesday, January 29, 2013

Brocade Switch: the CPU utilization data collected may have wrapped around and result in high utilization

Sometimes I have an issue when I see a very high utilization on a Brocade switch when doing a "show cpu-utilization" command.  Because it may report 99%, but anytime after I run that command, its always down to 1% (or so).  Why does it do that?  Well, I asked a Brocade engineer that I trust, and his reply was just what I thought (for the most part).  He said that the first % rating was pretty much bogus. He says the average values should be right, but the best idea is to run the command 2 or 3 times to get something accurate.  Im ok with that, as long as I know the first reported percentage rate may be bogus if its been a while since I ran the command.  Here is an example below:

telnet@Switch#sh cpu-utilization
99 percent busy, from 7200216 sec ago        <------------- Bogus % rating, run the command again
It's been more than 50 hours since last call, the CPU utilization data collected may have wrapped around and result in high utilization
1   sec avg:  1 percent busy         <------------- Should be correct
5   sec avg:  1 percent busy         <------------- Should be correct
60  sec avg:  1 percent busy         <------------- Should be correct
300 sec avg:  1 percent busy         <------------- Should be correct
telnet@Switch#sh cpu-utilization
1 percent busy, from 4 sec ago
1   sec avg:  1 percent busy
5   sec avg:  1 percent busy
60  sec avg:  1 percent busy
300 sec avg:  1 percent busy
telnet@Switch#sh cpu-utilization
1 percent busy, from 62 sec ago
1   sec avg:  1 percent busy
5   sec avg:  1 percent busy
60  sec avg:  1 percent busy
300 sec avg:  1 percent busy

Very interesting.

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