iRule latency stats

The CPU cycles per execution can be recorded by making the first line of the rule

 timing on 

and using the command

 show ltm rule  

More detail can be found in SOL6228: http://support.f5.com/kb/en-us/solutions/public/6000/200/sol6228.html

Instead of using the first-line/last-line when you try to calculate latency, you should use the first line of the first event (CLIENT_ACCEPTED, for example) and the last line of the last event (CLIENT_DATA or HTTP_REQUEST_RELEASE, for example), since the rule isn't going to necessarily execute top to bottom on every connection. Also, recording the timestamps and doing the math will certainly add to the traversal time of the packet.