Bug ID 680841: Reported Virtual Server CPU usage stats are slightly higher than actual

Last Modified: May 23, 2019

Bug Tracker

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

Known Affected Versions:
11.2.1, 11.4.0, 11.4.1, 11.5.0, 11.5.1, 11.5.1 HF1, 11.5.1 HF10, 11.5.1 HF11, 11.5.1 HF2, 11.5.1 HF3, 11.5.1 HF4, 11.5.1 HF5, 11.5.1 HF6, 11.5.1 HF7, 11.5.1 HF8, 11.5.1 HF9, 11.5.2, 11.5.2 HF1, 11.5.3, 11.5.3 HF1, 11.5.3 HF2, 11.5.4, 11.5.4 HF1, 11.5.4 HF2, 11.5.4 HF3, 11.5.4 HF4, 11.5.5, 11.5.6, 11.5.7, 11.5.8, 11.5.9, 11.6.0, 11.6.0 HF1, 11.6.0 HF2, 11.6.0 HF3, 11.6.0 HF4, 11.6.0 HF5, 11.6.0 HF6, 11.6.0 HF7, 11.6.0 HF8, 11.6.1, 11.6.1 HF1, 11.6.1 HF2, 11.6.2, 11.6.2 HF1, 11.6.3, 11.6.3.1, 11.6.3.2, 11.6.3.3, 11.6.3.4, 11.6.4, 12.0.0, 12.0.0 HF1, 12.0.0 HF2, 12.0.0 HF3, 12.0.0 HF4, 12.1.0, 12.1.0 HF1, 12.1.0 HF2, 12.1.1, 12.1.1 HF1, 12.1.1 HF2, 12.1.2, 12.1.2 HF1, 12.1.2 HF2, 12.1.3, 12.1.3.1, 12.1.3.2, 12.1.3.3, 12.1.3.4, 12.1.3.5, 12.1.3.6, 12.1.3.7, 12.1.4, 12.1.4.1, 13.0.0, 13.0.0 HF1, 13.0.0 HF2, 13.0.0 HF3, 13.0.1, 13.1.0, 13.1.0.1, 13.1.0.2, 13.1.0.3, 13.1.0.4, 13.1.0.5, 13.1.0.6, 13.1.0.7, 13.1.0.8, 13.1.1, 13.1.1.1, 13.1.1.2, 13.1.1.3, 13.1.1.4, 13.1.1.5, 14.0.0, 14.0.0.1, 14.0.0.2, 14.0.0.3, 14.0.0.4, 14.1.0, 14.1.0.1, 14.1.0.2, 14.1.0.3, 14.1.0.4, 14.1.0.5

Opened: Aug 29, 2017
Severity: 3-Major
Related AskF5 Article:
K67996855

Symptoms

The average CPU usage percentage reported per LTM Virtual Server is slightly higher than actual percentage of system CPU cycles used by each Virtual Server. The average CPU usage percentage per LTM Virtual Server is reported by the "tmsh show ltm virtual" and "tmctl virtual_server_cpu_stat" commands and in the GUI under "Statistics >> Module Statistics : Local Traffic >> Virtual Servers". The average CPU usage values reported by these commands incorrectly include TMM Idle cycles in the calculations, which causes a slight over-reporting of average per-Virtual-Server CPU usage.

Impact

Each LTM Virtual Server may appear to be using a greater percentage of system CPU cycles than they actually use.

Conditions

This occurs when LTM Virtual Server CPU usage stats are observed via the 'tmsh show ltm virtual' or 'tmctl virtual_server_cpu_stat' commands or in the GUI under Statistics :: Module Statistics : Local Traffic :: Virtual Servers.

Workaround

The instantaneous running count of TMM Idle cycles is displayed in the 'tm_idle_cycles' column displayed by the 'tmctl tmm_stat' command. This value can be compared to the 'tm_total_cycles' column to gain a general sense of the scale of the error. For a meaningful comparison of these values with the per-Virtual-Server CPU usage statistics (such as the 'avg_5sec' value reported by 'tmctl virtual_server_cpu_stat' or the 'Last 5 Seconds' value reported by 'tmsh show ltm virtual'), the 'tmctl tmm_stat' command should be run at intervals such as every 5 seconds, and the incremental changes in the 'tm_idle_cycles' and 'tm_total_cycles' values used to estimate the degree to which the per-Virtual-Server CPU usage percentage is over-reported.

Fix Information

None

Behavior Change