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_This readme is to help to get some powersave features running correctly on
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First: Pentium 4 CPUS are not designed for great energy saving issues. On
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current processors (as far as I know) there is only throttling available to
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decrease CPU performance and to save energy/heat production which is much less
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efficient than SpeedStep technologie provided on modern Pentium M processors.
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Note that there are also "Mobile Intel(R) Pentium(R) 4 - M CPU" (look in
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/proc/cpuinfo) which are different and which do support speedstepping.
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1) Be sure the processor module is loaded.
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Some machines might support additional C-(sleeping)states.
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Do: cat /proc/acpi/processor/*/power
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Are C2 or higher states supported? Fine you don't have to do anything, if your
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processor is idle, the kernel will take care that those states are activated
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-> just be sure the powersaved is running which loads the processor module at
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For Pentium 4 processors there are 2 interfaces supported by kernel:
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p4-clockmod module which exports the same files to /sys as cpufreq modules.
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and the "normal", acpi interface.
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Therefore you have two possibilities (none is set by default) to lower the
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energy output of your CPU:
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Do: cat /proc/acpi/processor/*/throttling
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If you get not supported goto 2)
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1) Use the PROCESSOR_DYNAMIC_LOW event (triggered when your CPU stays longer
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than 10 seconds below a specific CPU usage value (both are configurable)).
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Simply add throttle to the POWERSAVE_EVENT_PROCESSOR_DYNAMIC_LOW event in
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/etc/sysconfig/powersave/events and dethrottle to
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POWERSAVE_EVENT_PROCESSOR_DYNAMIC_HIGH (see README.events for more details)
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In case the dynamic low event is triggerd, your machine will be slowed down
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to the limit you set in your current scheme file (when on AC power
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scheme_performance by default). Also set the variable
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POWERSAVE_ALLOW_THROTTLING there.
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2) First check support by doing: modprobe p4-clockmod
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and: ls /sys/devices/system/cpu/cpufreq/ (must contain files).
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Set POWERSAVE_CPUFREQD_MODULE="p4-clockmod" in
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/etc/sysconfig/powersave/cpufreq and be sure you do not use the keyword
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"throttle" in the events config file (other interface -> double throttling
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can cause big trouble/slowdown)
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Now throttling is used as it would be Frequncy scaling.
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However you may experience your machine to be slower (specially when
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switching between windows very fast).
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Have a look into /etc/sysconfig/powersave/cpufreq config file and the
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README.cpufreq file to adjust the config values for better
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performance/powersavings.