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en:guides:cpu-frequency [2011/02/09 00:11] kultex |
en:guides:cpu-frequency [2011/02/09 18:48] linea tiny edits |
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==== Introduction ==== | ==== Introduction ==== | ||
- | To reduce power consumption is not only essential for portable computers, it is also essential to use it on desktop machines to reduce unnecessary CO2 emisson. You can save power by turning off not needed hardware components like WiFi, Bluetooth, etc., turning off or reduce monitor backlight, spinning down HDDs and controling CPU frequency. | + | To reduce power consumption is not only essential for portable computers: it is also essential to use it on desktop machines to reduce unnecessary CO2 emissions. You can save power by turning off not needed hardware components like WiFi, Bluetooth, etc., switching off or reducing the monitor backlight, spinning down HDDs and controlling the CPU frequency. |
- | CPU frequency scaling is built into 2.6 kernel and available, but because of Slitaz is very small and light, you have to install some additional tools and set it up by yourself. | + | CPU frequency scaling is built into the 2.6 kernel and available; but because Slitaz is very small and light, you have to install some additional tools and set it up by yourself. |
==== Installation ==== | ==== Installation ==== | ||
- | install linux-cpufreq, linux-acpi, cpufrequtils and optional powertop (for easy controling) - cpufrequtils and powertop we have to take from cooking, because cpufrequtils does not exist in 3.0 and powertop is buggy. | + | Install linux-cpufreq, linux-acpi, cpufrequtils and optional powertop (for easy controlling) - cpufrequtils and powertop we have to take from cooking, because cpufrequtils does not exist in 3.0 and powertop is buggy. |
<code># tazpkg get-install linux-cpufreq | <code># tazpkg get-install linux-cpufreq | ||
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==== Cpu driver ==== | ==== Cpu driver ==== | ||
- | you have to load the correct CPU kernel driver for your CPU - if you dont know, which CPU is in your PC you will get it from: | + | You have to load the correct CPU kernel driver for your CPU - if you don't know, which CPU is in your PC you can get it from: |
- | <file>cat /proc/cpuinfo</file> | + | <file> $ cat /proc/cpuinfo</file> |
- | Depending on the CPU, load one of the following modules - if you choose a wrong driver, you will get an error message, the module is not loaded and nothing goes wrong. | + | Depending on the CPU, load one of the following modules - if you choose the wrong driver, you will get an error message, the module is not loaded and nothing goes wrong. |
- | generic ACPI P-States based driver: | + | Generic ACPI P-States based driver: |
<code> # modprobe acpi-cpufreq</code> | <code> # modprobe acpi-cpufreq</code> | ||
AMD mobile K6-2/3+ PowerNow!: | AMD mobile K6-2/3+ PowerNow!: | ||
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AMD mobile Athlon PowerNow!: | AMD mobile Athlon PowerNow!: | ||
<code> # powernow-k7</code> | <code> # powernow-k7</code> | ||
- | AMD Cool&Quiet PowerNow!(up to AMD "K10" CPU) | + | AMD Cool&Quiet PowerNow!(up to AMD "K10" CPU): |
<code> # modprobe powernow-k8</code> | <code> # modprobe powernow-k8</code> | ||
Intel SpeedStep using the SMI BIOS interface: | Intel SpeedStep using the SMI BIOS interface: | ||
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Intel Enhanced SpeedStep (deprecated - use acpi-cpufreq): | Intel Enhanced SpeedStep (deprecated - use acpi-cpufreq): | ||
<code> # modprobe speedstep-centrino</code> | <code> # modprobe speedstep-centrino</code> | ||
- | Intel Pentium4/Xeon - The kernel documentation says "This adds the CPUFreq driver for Intel Pentium 4 / XEON processors. When enabled it will lower CPU temperature by skipping clocks. This driver should be only used in exceptional circumstances when very low power is needed because it causes severe slowdowns and noticeable latencies. Normally Speedstep should be used instead." - the p4-clockmod supports only performance and powersave governors (due to long transition latency of the module itself) | + | Intel Pentium4/Xeon - The kernel documentation says "This adds the CPUFreq driver for Intel Pentium 4 / XEON processors. When enabled it will lower CPU temperature by skipping clocks. This driver should be only used in exceptional circumstances when very low power is needed because it causes severe slowdowns and noticeable latencies. Normally Speedstep should be used instead." - the p4-clockmod supports only performance and powersave governors (due to the long transition latency of the module itself): |
<code> # modprobe p4-clockmod</code> | <code> # modprobe p4-clockmod</code> | ||
NatSemi Geode GX / Cyrix MediaGXm: | NatSemi Geode GX / Cyrix MediaGXm: | ||
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Manually configured clock speeds by user | Manually configured clock speeds by user | ||
- | the built in governors must not be loaded - the others must be loaded with modprobe - you may load as many governors as desired (only one will be active at any given time). | + | The built in governors must not be loaded - the others must be loaded with modprobe - you may load as many governors as desired (only one will be active at any given time). |
- | Remains the question, which governor saves most energy? The Powersave governor will only save you power if you're playing 3D games (it does not save power because application process completion times are prolonged at the lower processor frequency and the system does not enter a deep C-state. The greatest power savings occur at idle in deeper C-states) and the performance governor will basically never give you extra performance. Don't use them - therfore I am not happy that the performance governor is used as default in SliTaz. So you might choose between ondemand and conservative, which is a matter of taste. | + | Which poses the question, which governor saves most energy? The Powersave governor will only save you power if you're playing 3D games (it does not save power because application process completion times are prolonged at the lower processor frequency and the system does not enter a deep C-state. The greatest power savings occur at idle in deeper C-states) and the performance governor will basically never give you extra performance. Don't use them - therefore I am not happy that the performance governor is used by default in SliTaz. So you might choose between ondemand and conservative, which is a matter of taste. |
- | The userspace governor is necessary for third party applications - like cpupowerd http://www.themaxer.com/index.php?option=com_content&view=article&id=86:undervolting-your-cpu&catid=41:nas&Itemid=81 - unfortunally it does not work in SliTaz, because the kernel config for CONFIG_X86_MSR is not set | + | The userspace governor is necessary for third party applications - like cpupowerd http://www.themaxer.com/index.php?option=com_content&view=article&id=86:undervolting-your-cpu&catid=41:nas&Itemid=81 - unfortunately it does not work in SliTaz, because the kernel config for CONFIG_X86_MSR is not set. |
==== Select the governor ==== | ==== Select the governor ==== | ||
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Use the 'cpufreq-set' command to activate one of the governors - for example: | Use the 'cpufreq-set' command to activate one of the governors - for example: | ||
- | cpufreq-set -g ondemand | + | <code> # cpufreq-set -g ondemand</code> |
- | Please note, if you have a dual-core or multiple-core CPU, you must specify explicitely the CPU. There are CPU's where each core can run with different setting! Example for a dual-core CPU: | + | Please note, if you have a dual-core or multiple-core CPU, you must explicitly specify the CPU. There are CPU's where each core can run with different settings! Example for a dual-core CPU: |
- | cpufreq-set -c 0 -c 1 -g conservative | + | <code> # cpufreq-set -c 0 -c 1 -g conservative</code> |