Linux gives TSC skew messages during boot process - IBM eServer xSeries 460 and MXE 460

Resolving The Problem

RETAIN tip: H186773

The following message is displayed during boot up of a Linux operating system. "BIOS Bug:CPU#xx improperly initialized, has #### usecs TSC skew"

The system may be any of the following IBM servers:

• IBM eServer xSeries MXE 460, Type 8874, any model
• IBM eServer xSeries 460, Types 8874 and 8872, any model

The system is configured with >4 processors.

The system is configured with any diagnostics.

• any

The Firmware level(s) affected is/are:

• any

The following network operating systems are affected:

• SuSE Linux Enterprise Server X

Note: This does not imply that the network operating system will work under all combinations of hardware and software.

Please see the compatibility page for more information:

http://www.ibm.com/servers/eserver/serverproven/compat/us/

None.

The message should be ignored.

Current Intel processors have a TSC (time stamp counter). This is a counter which increments on each pulse of the clock signal. Many operating systems use this for a high precision timer. On multiprocessor boxes Linux attempt to synchronize the TSC's within all the processors at startup. By doing so, if a running process makes use of the tsc to obtain timing information it will receive the correct information even it has been migrated between processors while checking the value in the TSC. A IBM eServer xSeries 460 multi-node environment there are multiple front side buses (FSB's). These buses do not share a common clock source. As such the TSC's within processors on separate FSB's will drift apart from each other gradually over time. Linux notices this drift on initialization and attempts to correct it under the assumption that the system BIOS did not do so when it originally initialized the processors. This is an erroneous (but harmless) assumption and subsequent action. Further, current versions of Linux use alternate mechanisms for high precision timers. In the case of a box with multiple FSB's, this warning is an artifact and should be removed in new versions of the Linux kernel.