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diff --git a/Documentation/cpu-freq/user-guide.txt b/Documentation/cpu-freq/user-guide.txt new file mode 100644 index 000000000..ff2f28332 --- /dev/null +++ b/Documentation/cpu-freq/user-guide.txt @@ -0,0 +1,224 @@ + CPU frequency and voltage scaling code in the Linux(TM) kernel + + + L i n u x C P U F r e q + + U S E R G U I D E + + + Dominik Brodowski <linux@brodo.de> + + + + Clock scaling allows you to change the clock speed of the CPUs on the + fly. This is a nice method to save battery power, because the lower + the clock speed, the less power the CPU consumes. + + +Contents: +--------- +1. Supported Architectures and Processors +1.1 ARM +1.2 x86 +1.3 sparc64 +1.4 ppc +1.5 SuperH +1.6 Blackfin + +2. "Policy" / "Governor"? +2.1 Policy +2.2 Governor + +3. How to change the CPU cpufreq policy and/or speed +3.1 Preferred interface: sysfs + + + +1. Supported Architectures and Processors +========================================= + +1.1 ARM +------- + +The following ARM processors are supported by cpufreq: + +ARM Integrator +ARM-SA1100 +ARM-SA1110 +Intel PXA + + +1.2 x86 +------- + +The following processors for the x86 architecture are supported by cpufreq: + +AMD Elan - SC400, SC410 +AMD mobile K6-2+ +AMD mobile K6-3+ +AMD mobile Duron +AMD mobile Athlon +AMD Opteron +AMD Athlon 64 +Cyrix Media GXm +Intel mobile PIII and Intel mobile PIII-M on certain chipsets +Intel Pentium 4, Intel Xeon +Intel Pentium M (Centrino) +National Semiconductors Geode GX +Transmeta Crusoe +Transmeta Efficeon +VIA Cyrix 3 / C3 +various processors on some ACPI 2.0-compatible systems [*] + +[*] Only if "ACPI Processor Performance States" are available +to the ACPI<->BIOS interface. + + +1.3 sparc64 +----------- + +The following processors for the sparc64 architecture are supported by +cpufreq: + +UltraSPARC-III + + +1.4 ppc +------- + +Several "PowerBook" and "iBook2" notebooks are supported. + + +1.5 SuperH +---------- + +All SuperH processors supporting rate rounding through the clock +framework are supported by cpufreq. + +1.6 Blackfin +------------ + +The following Blackfin processors are supported by cpufreq: + +BF522, BF523, BF524, BF525, BF526, BF527, Rev 0.1 or higher +BF531, BF532, BF533, Rev 0.3 or higher +BF534, BF536, BF537, Rev 0.2 or higher +BF561, Rev 0.3 or higher +BF542, BF544, BF547, BF548, BF549, Rev 0.1 or higher + + +2. "Policy" / "Governor" ? +========================== + +Some CPU frequency scaling-capable processor switch between various +frequencies and operating voltages "on the fly" without any kernel or +user involvement. This guarantees very fast switching to a frequency +which is high enough to serve the user's needs, but low enough to save +power. + + +2.1 Policy +---------- + +On these systems, all you can do is select the lower and upper +frequency limit as well as whether you want more aggressive +power-saving or more instantly available processing power. + + +2.2 Governor +------------ + +On all other cpufreq implementations, these boundaries still need to +be set. Then, a "governor" must be selected. Such a "governor" decides +what speed the processor shall run within the boundaries. One such +"governor" is the "userspace" governor. This one allows the user - or +a yet-to-implement userspace program - to decide what specific speed +the processor shall run at. + + +3. How to change the CPU cpufreq policy and/or speed +==================================================== + +3.1 Preferred Interface: sysfs +------------------------------ + +The preferred interface is located in the sysfs filesystem. If you +mounted it at /sys, the cpufreq interface is located in a subdirectory +"cpufreq" within the cpu-device directory +(e.g. /sys/devices/system/cpu/cpu0/cpufreq/ for the first CPU). + +cpuinfo_min_freq : this file shows the minimum operating + frequency the processor can run at(in kHz) +cpuinfo_max_freq : this file shows the maximum operating + frequency the processor can run at(in kHz) +cpuinfo_transition_latency The time it takes on this CPU to + switch between two frequencies in nano + seconds. If unknown or known to be + that high that the driver does not + work with the ondemand governor, -1 + (CPUFREQ_ETERNAL) will be returned. + Using this information can be useful + to choose an appropriate polling + frequency for a kernel governor or + userspace daemon. Make sure to not + switch the frequency too often + resulting in performance loss. +scaling_driver : this file shows what cpufreq driver is + used to set the frequency on this CPU + +scaling_available_governors : this file shows the CPUfreq governors + available in this kernel. You can see the + currently activated governor in + +scaling_governor, and by "echoing" the name of another + governor you can change it. Please note + that some governors won't load - they only + work on some specific architectures or + processors. + +cpuinfo_cur_freq : Current frequency of the CPU as obtained from + the hardware, in KHz. This is the frequency + the CPU actually runs at. + +scaling_available_frequencies : List of available frequencies, in KHz. + +scaling_min_freq and +scaling_max_freq show the current "policy limits" (in + kHz). By echoing new values into these + files, you can change these limits. + NOTE: when setting a policy you need to + first set scaling_max_freq, then + scaling_min_freq. + +affected_cpus : List of Online CPUs that require software + coordination of frequency. + +related_cpus : List of Online + Offline CPUs that need software + coordination of frequency. + +scaling_driver : Hardware driver for cpufreq. + +scaling_cur_freq : Current frequency of the CPU as determined by + the governor and cpufreq core, in KHz. This is + the frequency the kernel thinks the CPU runs + at. + +bios_limit : If the BIOS tells the OS to limit a CPU to + lower frequencies, the user can read out the + maximum available frequency from this file. + This typically can happen through (often not + intended) BIOS settings, restrictions + triggered through a service processor or other + BIOS/HW based implementations. + This does not cover thermal ACPI limitations + which can be detected through the generic + thermal driver. + +If you have selected the "userspace" governor which allows you to +set the CPU operating frequency to a specific value, you can read out +the current frequency in + +scaling_setspeed. By "echoing" a new frequency into this + you can change the speed of the CPU, + but only within the limits of + scaling_min_freq and scaling_max_freq. |