Power Saving BIOS Setting OS Control

Dell

9.3.2Power Saving BIOS Setting (OS Control)

Intel processors support Demand Based Switching (DBS) which enables the processor to dynamically change its operating frequency in response to workload changes. The industry standard implementation of this power management feature is in the Operating System (OS). The OS monitors process/thread level utilization of the processor and uses processor controls to change the processor’s operating frequency. For heavy workloads, the OS will run the processor at higher frequencies for additional performance. Lighter workloads do not need high performance, thus the OS will run the processor at lower frequencies.

9.3.3Maximum Performance

The Maximum Performance Mode disables power management. In this mode, the processor frequency is statically set to the highest supported frequency.

The power management features are implemented via two categories: fixed or generic. Fixed features use bits defined in the ACPI specification for specific capabilities. The fixed feature bits give the OS complete control over the power management of a device since the location of the bits is given to the OS in the FACP table. Thus, a driver can directly access bits to control a device’s power management. Generic features have defined enable and status bits, but the functionality is not fully visible to the OS. Dell provides ASL code to handle the details of generic features, allowing the OS to intelligently communicate with system-specific hardware.

Table 15. Summary of R210 Power Management Features

Feature	Type	Enable/Status	Description
		/Ctrl bit
		location

ACPI mode	Fixed	PCH	The OS uses the SCI_EN bit to switch from
switch			legacy mode to ACPI mode.

Sleep states	Fixed	PCH	Supported states: S0(Working), S4-OS
			(‘Hibernation’ in W2K), and S5 (Soft-off).
			S1 (also called ‘standby’ or ‘suspend’) and S3
			are not supported.

Power Button	Fixed	PCH	In ACPI mode, OS has control of the power
			button. In non-ACPI mode, SMI handler owns
			power button events.

Real-Time	Fixed	PCH	The OS is able to configure the system to wake
Clock			on the RTC alarm.

Power Mgmt.	Fixed	PCH	24-bit power management timer is used.
Timer

Power Mgmt.	Generic	PCH	Each host bus’s PME# signal is routed to a
Event (PME)			separate general-purpose event pin in the
			chipset. When a device signals PME#, the system
			wakes (if necessary), the OS detects the event,
			and a Dell defined ASL routine handles the
			event. Wake-on-LAN is one example of a PME.

PowerEdge R210 Technical Guide