Changing uEFI/BIOS F1 settings while in the "Custom" Operating Mode may cause the allowable power capping range to be too low or too high - IBM BladeCenter HS22V, System x3850 X5

Resolving The Problem

Source

RETAIN tip: H196749

Symptom

The power management firmware on IBM System x servers provides a platform power capping functionality that can be used to limit the server to a maximum configurable system power consumption value. There are upper and lower limits to the power cap value that the power management firmware can enforce. These limits are dependent on the current hardware and firmware configuration in such a way that they must be determined dynamically whenever a hardware or firmware change is detected during the platform boot process.

If certain Unified Extensible Firmware Interface (UEFI) / Basic Input/Output System (BIOS) F1 Setup changes are made, the power management firmware may not detect the change, and the upper and lower limits for the power cap value will not be updated to reflect the new configuration.

This issue only appears on servers that have enabled power capping in the UEFI/BIOS F1 Setup Menu. Power capping is enabled by selecting Settings, Power Active Energy Manager, and Capping Enabled.

If either the memory speed or QPI link frequency is changed and no other changes were made in the F1 Setup Menu, then the power management firmware will not attempt to re-evaluate the upper and lower power capping limits.

Affected configurations

The system may be any of the following IBM servers:

• BladeCenter HS22V, type 1949, any model
• BladeCenter HS22V, type 7871, any model
• System x3850 X5, type 7145, any model
• System x3850 X5, type 7146, any model
• System x3950 X5, type 7145, any model

This tip is not software specific.

This tip is not option specific.

The following system BIOS level(s) are affected:

• Release 1.07 - Build ID P9E146AUS
  

Solution

This behavior will be corrected in a future release of UEFI firmware.

The target date for this release is scheduled for Second Quarter 2010.

The file will be available by selecting the appropriate machine type on the 'Software and device drivers - IBM System x' web page, at the following URL:

The fix will automatically detect all appropriate UEFI settings changes and update the power capping range accordingly, so no workaround steps will be necessary.

Workaround

This issue will only occur if the "Memory Speed" or "QPI Link Frequency" settings are changed individually. Therefore, the issue can be avoided by choosing UEFI Operating Modes (Settings --> Operating Modes) to effect the desired change.

If the "Memory Speed" or "QPI Link Frequency" settings must be changed individually, then a re-evaluation of the lower and upper power capping limits can be forced by simultaneously changing another UEFI setting that is known to correctly cause this re-evaluation. UEFI settings currently known to cause this re-evaluation are Settings --> Processors --> Turbo Mode and Settings --> Processors --> Hyper-Threading.

Additional information

In order to determine an accurate power capping range bounded by lower and upper power capping limits, the power management firmware executes a maximum utilization workload during system boot in order to analyze the power response. This power maximization workload is only executed when a hardware or UEFI/BIOS setting change occurs that might affect system power consumption. The "Memory Speed" and "QPI Link Frequency" settings may affect system power consumption, but due to the issue described here, changes in these settings do not trigger a re-run of the power maximization workload. Thus, the power capping range is not updated when these settings are changed and the power capping range may be seen to slightly deviate from the actual system power response.

Other UEFI/BIOS settings such as "Turbo Mode" and "Hyper-Threading" have been confirmed to correctly trigger a re-run of the power maximization workload. Thus, as long as these settings are modified in addition to the "Memory Speed" or "QPI Link Frequency" settings, then the power maximization workload will be executed during the next system boot and the inaccurate power capping range issue will be avoided. In addition, changes to the UEFI "Operating Mode" setting cause the power capping range to be re-evaluated, so if this setting is used to indirectly affect the "Memory Speed" and "QPI Link Frequency" settings (assuming "Custom mode" is not selected), then the power maximization workload will be executed and the issue will likewise be avoided.

If the issue has already occurred, then the inaccurate power capping range can be corrected by forcing a re-run of the power maximization workload. This is accomplished by changing any of the settings that are known to trigger the workload. The workload is then executed with whatever UEFI/BIOS settings are currently chosen, so any previous changes to the "Memory Speed" or "QPI Link Frequency" settings will affect the workload while it is running. When the workload executes, the power consumed by the currently configured system will be evaluated and an accurate power capping range will be established.