Table of Contents
Advertisement
technology, which is a major feature of the processors in the x3850 M2 and
x3950 M2 servers.
Lowering the processor performance state when processor demand is low can
significantly reduce CPU dynamic power consumption. These processor
performance states can be changed very quickly in response to processor
demand while software continues to execute. This technique, sometimes referred
to as demand-based switching (DBS), allows the operating system to provide
automatic scaling of the processor's power consumption in response to varying
workloads, with no required user intervention and no perceivable effect to system
performance.
The number of P-states depends on the type of processor. This information is
defined in the ACPI table of the BIOS. The operating system reads the ACPI
information and adjusts the core voltage followed by the core frequency, while the
processor continues to run. The Processor Performance States option (shown in
Figure 3-9 on page 100) is disabled by default; you enable it in BIOS.
The following sections show examples in Linux, Windows Server 2003, Windows
2008, and how you can identify the operating system power management
Linux
Various distributions of Linux operating systems, such as SUSE SLES10/SP2 or
RHEL5U2 based on kernel 2.6, integrate power management features by default.
The kernel processor frequency scaling subsystem can adjust the core
frequency as it goes. After the P-states are enabled in the BIOS, the subdevice is
found in the operating system at the following location:
/sys/devices/system/cpu/cpu0/cpufreq
To show the available core frequencies, which are adjustable, use the cat
command, shown in Example 3-1.
Example 3-1 Command to show available core frequencies
# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
2128000 1862000 1862000 1596000
#
The command can also show the current value of the core frequency, as
indicated in Example 3-2.
Example 3-2 Command to show current core frequency
# cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
1596000
#
102
Planning, Installing, and Managing the IBM System x3950 M2
Advertisement
Table of Contents
