Bug ID 446398: System CPU usage may be misleading

Last Modified: Apr 10, 2019

Bug Tracker

Affected Product:  See more info
BIG-IP LTM(all modules)

Known Affected Versions:
11.5.0

Fixed In:
11.5.1

Opened: Jan 27, 2014
Severity: 2-Critical

Symptoms

On BIG-IP 11.5.0, the overall system CPU usage may not accurately indicate how much of the CPU resources are used, or more importantly how much headroom is left. The system CPU usage may be reported lower than it should be.

Impact

A BIG-IP may not have as much unused CPU capacity as it appears. Commands such as "top" will not report correct idle numbers.

Conditions

This occurs on a BIG-IP platform that supports Intel hyper-threads.

Workaround

Check the CPU usage for all blades and average only the odd or even cores, whichever are higher, to get a more accurate indication of CPU usage.

Fix Information

F5 has improved accuracy of CPU measurements across all loads and has increased the general product stability at high loads. CPU measurements at medium-high loads (75%) may read slightly higher CPU than previously release but they are more accurate (linear) and the box is much more manageable and stable at higher loads. The combination of these two should not invalidate any previous sizing decisions.

Behavior Change