frequent update_cpu_power messages in the system logs

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Environment

SUSE Linux Enterprise Server 11 Service Pack 1 (SLES 11 SP1)
SUSE Linux Enterprise Server 11 Service Pack 2 (SLES 11 SP2)

Situation

Log messages relating to update_cpu_power appear frequently in the system logs:

Jun 6 13:17:12 myhost kernel: [87824625.772466] update_cpu_power: cpu_power = 28614818560; scale_rt = 49748003745
Jun 6 13:17:12 myhost kernel: [51795828.865150] update_cpu_power: cpu_power = 24528796992; scale_rt = 42644292225
Jun 6 13:17:12 myhost kernel: [87824626.024221] update_cpu_power: cpu_power = 21251351804; scale_rt = 36946323002
Jun 6 13:17:12 myhost kernel: [87824626.036207] update_cpu_power: cpu_power = 20892174701; scale_rt = 36321879278
Jun 6 13:17:14 myhost kernel: [87824627.762462] update_cpu_power: cpu_power = 28542184816; scale_rt = 49621727084

These messages may have non-consecutive timestamps.

In the example above, it can be seen that the timestamps from the kernel are not
all consecutive.

Jun 6 13:17:12 myhost kernel: [87824625.772466]
Jun 6 13:17:12 myhost kernel: [51795828.865150]
Jun 6 13:17:12 myhost kernel: [87824626.024221]

Resolution

Update to SLES 11 SP3 or later, which is not effected by this issue.

SLES 11 SP2 is not effected by the issue, however a patch has been provided as a
precautionary measure in kernel-3.0.101-0.7.19.1, which is available to customers with
Long Term Service Pack Support (LTSS).

Customers who have LTSS for SLES 11 SP1 can update to kernel-2.6.32.59-0.13.1 or later.

Cold booting the system at a minimum of every 208 days should avoid the issue.

Cause

Additional Information

Additional checks were put in place to protect scale_rt_power() from clock
aberrations, and also to prevent any anomalous value returned by scale_rt_power()
from being stored in load balancing structures to be encountered at some later time.

As a safety measure was implemented to avoid potential overflows in the clocksource.

Also, changes were made to limit the number of update_cpu_power messages that would
be logged.

Disclaimer

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