System information

Power Management 151
In case of a CPU upgrade, make sure to upgrade your BIOS, too. The BIOS needs
to know the new CPU and its valid frequencies steps in order to pass this infor-
mation on to the operating system.
CPUfreq subsystem enabled?
In SUSE Linux Enterprise Server, the CPUfreq subsystem is enabled by default.
To find out if the subsystem is currently enabled, check for the following path
in your system: /sys/devices/system/cpu/cpufreq (or /sys/de
vices/system/cpu/cpu*/cpufreq for machines with multiple cores). If
the cpufreq subdirectory exists, the subsystem is enabled.
Log file information?
Check syslog (usually /var/log/messages) for any output regrading the
CPUfreq subsystem. Only severe errors are reported there.
If you suspect problems with the CPUfreq subsystem on your machine, you can
also enable additional debug output. To do so, either use cpufreq.debug=7
as boot parameter or execute the following command as root:
echo 7 > /sys/module/cpufreq/parameters/debug
This will cause CPUfreq to log more information to dmesg on state transitions,
which is useful for diagnosis. But as this additional output of kernel messages can
be rather comprehensive, use it only if you are fairly sure that a problem exists.
11.7 For More Information
• A threepart, comprehensive article about tuning components with regards to power
efficiency is available at the following URLs:
• Reduce Linux power consumption, Part 1: The CPUfreq subsystem, avail-
able at http://www.ibm.com/developerworks/linux/li
brary/l-cpufreq-1/?ca=dgr-lnxw03ReduceLXPWR-P1dth-
LX&S_TACT=105AGX59&S_CMP=grlnxw03
• Reduce Linux power consumption, Part 2: General and governor-specific set-
tings, available at http://www.ibm.com/developerworks/lin
ux/library/l-cpufreq-2/?ca=dgr-lnxw03ReduceLXPWR-
P1dth-LX&S_TACT=105AGX59&S_CMP=grlnxw03
• Reduce Linux power consumption, Part 3: Tuning results, available
at http://www.ibm.com/developerworks/linux/li