Issue

The Cisco CSS is showing a high level of CPU usage, even though the networking throughput does not appear excessively high nor is there a large number of EQL or DQL`s configured.

CSS11501# sh system-resources cpu
Chassis CPU Utilizations
Module Name Module 5Sec 1Min 5Min
----------------------------------------------------
CSS501-SCM-INT 1 90% 88% 75%
CSS501-SSL-C-INT 2 0% 0% 0%

Solution

Though there can be a number of causes to high CPU, within this article we look at the CPU resource consumption being due to the flow table.
Due to a high level of connections transversing the CSS the LoadBalancer uses CPU resource to build the subsequent flows within the flow table.
A typically example being DNS traffic. The following example shows the required commands need to disable flow created for UDP/53.

flow-state 53 udp flow-disable nat-enable