irule timing: how to convert Cycles to Seconds

| Cycles (min, avg, max) = (40435, 83870, 148659)

 

 

First off, you'll want more than 10 iterations of the rule to get a good average. The Min and Max aren't really applicable and can greatly throw off the average. You'll notice as you run this rule more times that the average will float to a lower and more stable number because the Max number isn't throwing it off as much.

 

 

The numbers you are seeing here correlate to the number of CPU cycles used to execute this rule. Divide by the number of cycles available on the model LTM you are running. For instance if you were running on an LTM 6800 (with a 2.4ghz proc) you would divide 2,400,000,000 by 83,870. This rule could theoretically fire 28k times per second before overrunning the CPU. Stated another way, the rule takes up .0035 percent of a one second time slice of the CPU.

 

 

Keep in mind that the LTM is using the CPU for many purposes, including basic load balancing and processing of packets. If your CPU was at %30 before with a maximum of 1,000 new connections per second, then adding the iRule will bump the LTMs CPU to %30 + (1000 * .0035) = %33.5