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wiki:cpu_frequency_scaling_basics [2011/09/30 23:20] – added some linebreaks littlebatwiki:cpu_frequency_scaling_basics [2014/12/26 06:43] (current) – bmarkus
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 To reduce power consumption is essential for portable computers but there are no reason not to use on desktop machines. You can save power turning off not needed hardware components like WiFi, Bluetooth, turning off or reduce monitor backlight, spinning down HDD and to control CPU frequency. To reduce power consumption is essential for portable computers but there are no reason not to use on desktop machines. You can save power turning off not needed hardware components like WiFi, Bluetooth, turning off or reduce monitor backlight, spinning down HDD and to control CPU frequency.
  
-CPU frequency scaling is built into 2.6 kernel and available with Tiny Core also, but you need few additional tools and you have to setup it yourself. Most of the modern CPU's and chipsets support frequency scaling, there is a high chance that you can use it.+TC4 activates CPU frequency scaling by default at startup time in case of suitable CPU found and enables 'ondemand' governor, which will select automatically frequency based on applications demand.
  
-It is a short introductory article how to enable and use it. There are plenty of additional recources on the net.+In most cases it works fine and you do not need any additional action.
  
- +However, as there are certain setups where either not all required drivers are automatically loaded and/or where the 'ondemand' governor gets prevented from being enabled (due to latency being too high), it is a good idea to do a check - based on info which follows - whenever running TC4 for the first time with a specific processor or chipset.
-===== #TOOLS REQUIRED ===== +
- +
-You need the cpufreq.tcz extension and its dependencies from the repository. +
- +
- +
-===== #CPU DRIVER ===== +
- +
-Next you have to load the proper CPU kernel driver matching your CPU. To identify the CPU type in a terminal window: +
- +
-cat /proc/cpuinfo +
- +
-Depending on the CPU, load one of the following modules with the 'modprobe' command: +
- +
-p4-clockmod (Intel) +
-powernow-k6 (AMD K6) +
-powernow-k7 (AMD K7) +
-powernow-k8 (AMD K8) +
-longhaul    (VIA Nehemiah) +
- +
-If you choose a wrong driver you will get an error message and module is not loaded, nothing goes wrong. +
- +
-Alternatively you can try +
- +
-acpi-cpufreq +
- +
-It is not so efficient as CPU specific modules, but better than nothing. +
- +
-There are drivers for certain chipsets not only for CPU's but it is out of the scope of this introduction.+
  
  
 ===== #VIEW CPU FREQUENCY INFORMATION ===== ===== #VIEW CPU FREQUENCY INFORMATION =====
  
-Now you can check actual CPU frequency and other information. Type in a terminal window:+If you want to view actual CPU frequency settings, install cpufrequtils.tcz extension and use command:
  
 cpufreq-info cpufreq-info
  
-and you will get a similar screen: 
  
-{{"http://tc.hasix.org/scrcap/cpufreqinfo1.png"}} 
  
  
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 userspace - allows userspace programs (or any process running as root) to set the frequency userspace - allows userspace programs (or any process running as root) to set the frequency
  
-Above governors are modules, loaded automatically when needed, but you can modprobe them before using. Default is performance.+Above governors are modules, loaded automatically when needed, but you can modprobe them before using. TC default is 'ondemand'.
  
-For most systems, the Ondemand governor can provide the best compromise between heat emission, power consumption, performance, and manageability. When the system is only busy at specific times of the day, the Ondemand governor will automatically switch between maximum and minimum frequency depending on the load without any further intervention.+For most systems, the 'ondemand' governor can provide the best compromise between heat emission, power consumption, performance, and manageability. When the system is only busy at specific times of the day, the 'ondemand' governor will automatically switch between maximum and minimum frequency depending on the load without any further intervention.
  
  
-===== #SELECT GOVERNOR =====+===== #CHANGING GOVERNOR =====
  
-At this point everything is prepared but no active governor selected and no running third party daemon installed, so no any power saving yet.+If you want to use a different governor the 'ondemand', install cpufreq-utils.tcz extension.
  
 Use the 'cpufreq-set' command to activate one of the governors mentioned above, for example: Use the 'cpufreq-set' command to activate one of the governors mentioned above, for example:
  
-cpufreq-set -g ondemand+cpufreq-set -g performance
  
 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 specify explicitely the CPU. There are CPU's where each core can run with different setting! Example for a dual-core CPU:
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 ===== #USER SPACE PROGRAMS ===== ===== #USER SPACE PROGRAMS =====
  
-There are user space programs to manage not only cpu frequency but other components also. One of those, cpufreqd is part of the cpufreq.tcel/tcpufreq.tcz extension installed.+There are user space programs to manage not only cpu frequency but other components also. One of those, cpufreqd is available in the repository. 
 + 
 + 
 +===== #TROUBLESHOOTING =====
  
-For the curious there are many good articles on the net.+The following relates to a Pentium M under TC3.8.4 (2.6.33.3 kernel) running on a Dell Precision M70\\ 
 +laptop, but may still be applicable if you run into a similiar problem.\\ 
 +Installed cpufrequtils and selected ondemand govenor. The policy line from the cpufreq-info command read:\\ 
 +<code>current policy: frequency should be within 800 MHz and 800 MHz.</code> 
 +indicated that CPU was locked at 800Mhz. Executing the command: 
 +<code>cat /sys/devices/system/cpu/cpu0/cpufreq/bios_limit</code> 
 +returned the value 800000 (frequency in Khz). Using the boot code: 
 +<code>processor.ignore_ppc=1</code> 
 +fixed that. Now bios_limit contains 2267000 (2.267Ghz), the maximum speed for this CPU. Checking\\ 
 +\proc\cpuinfo several times showed that the frequency was bouncing between 800Mhz and 2.27Ghz\\ 
 +even though the machine was not doing anything. Changing the governor to conservative fixed that.\\ 
 +For links to bug reports that helped solve this problem, see:\\ 
 +http://forum.tinycorelinux.net/index.php/topic,14917.msg85013.html#msg85013
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