1 CPU frequency and voltage scaling code in the Linux(TM) kernel 2 3 4 L i n u x C P U F r e q 5 6 U S E R G U I D E 7 8 9 Dominik Brodowski <linux@brodo.de> 10 11 12 13 Clock scaling allows you to change the clock speed of the CPUs on the 14 fly. This is a nice method to save battery power, because the lower 15 the clock speed, the less power the CPU consumes. 16 17 18Contents: 19--------- 201. Supported Architectures and Processors 211.1 ARM 221.2 x86 231.3 sparc64 241.4 ppc 251.5 SuperH 261.6 Blackfin 27 282. "Policy" / "Governor"? 292.1 Policy 302.2 Governor 31 323. How to change the CPU cpufreq policy and/or speed 333.1 Preferred interface: sysfs 343.2 Deprecated interfaces 35 36 37 381. Supported Architectures and Processors 39========================================= 40 411.1 ARM 42------- 43 44The following ARM processors are supported by cpufreq: 45 46ARM Integrator 47ARM-SA1100 48ARM-SA1110 49Intel PXA 50 51 521.2 x86 53------- 54 55The following processors for the x86 architecture are supported by cpufreq: 56 57AMD Elan - SC400, SC410 58AMD mobile K6-2+ 59AMD mobile K6-3+ 60AMD mobile Duron 61AMD mobile Athlon 62AMD Opteron 63AMD Athlon 64 64Cyrix Media GXm 65Intel mobile PIII and Intel mobile PIII-M on certain chipsets 66Intel Pentium 4, Intel Xeon 67Intel Pentium M (Centrino) 68National Semiconductors Geode GX 69Transmeta Crusoe 70Transmeta Efficeon 71VIA Cyrix 3 / C3 72various processors on some ACPI 2.0-compatible systems [*] 73 74[*] Only if "ACPI Processor Performance States" are available 75to the ACPI<->BIOS interface. 76 77 781.3 sparc64 79----------- 80 81The following processors for the sparc64 architecture are supported by 82cpufreq: 83 84UltraSPARC-III 85 86 871.4 ppc 88------- 89 90Several "PowerBook" and "iBook2" notebooks are supported. 91 92 931.5 SuperH 94---------- 95 96The following SuperH processors are supported by cpufreq: 97 98SH-3 99SH-4 100 1011.6 Blackfin 102------------ 103 104The following Blackfin processors are supported by cpufreq: 105 106BF522, BF523, BF524, BF525, BF526, BF527, Rev 0.1 or higher 107BF531, BF532, BF533, Rev 0.3 or higher 108BF534, BF536, BF537, Rev 0.2 or higher 109BF561, Rev 0.3 or higher 110BF542, BF544, BF547, BF548, BF549, Rev 0.1 or higher 111 112 1132. "Policy" / "Governor" ? 114========================== 115 116Some CPU frequency scaling-capable processor switch between various 117frequencies and operating voltages "on the fly" without any kernel or 118user involvement. This guarantees very fast switching to a frequency 119which is high enough to serve the user's needs, but low enough to save 120power. 121 122 1232.1 Policy 124---------- 125 126On these systems, all you can do is select the lower and upper 127frequency limit as well as whether you want more aggressive 128power-saving or more instantly available processing power. 129 130 1312.2 Governor 132------------ 133 134On all other cpufreq implementations, these boundaries still need to 135be set. Then, a "governor" must be selected. Such a "governor" decides 136what speed the processor shall run within the boundaries. One such 137"governor" is the "userspace" governor. This one allows the user - or 138a yet-to-implement userspace program - to decide what specific speed 139the processor shall run at. 140 141 1423. How to change the CPU cpufreq policy and/or speed 143==================================================== 144 1453.1 Preferred Interface: sysfs 146------------------------------ 147 148The preferred interface is located in the sysfs filesystem. If you 149mounted it at /sys, the cpufreq interface is located in a subdirectory 150"cpufreq" within the cpu-device directory 151(e.g. /sys/devices/system/cpu/cpu0/cpufreq/ for the first CPU). 152 153cpuinfo_min_freq : this file shows the minimum operating 154 frequency the processor can run at(in kHz) 155cpuinfo_max_freq : this file shows the maximum operating 156 frequency the processor can run at(in kHz) 157scaling_driver : this file shows what cpufreq driver is 158 used to set the frequency on this CPU 159 160scaling_available_governors : this file shows the CPUfreq governors 161 available in this kernel. You can see the 162 currently activated governor in 163 164scaling_governor, and by "echoing" the name of another 165 governor you can change it. Please note 166 that some governors won't load - they only 167 work on some specific architectures or 168 processors. 169 170cpuinfo_cur_freq : Current speed of the CPU, in KHz. 171 172scaling_available_frequencies : List of available frequencies, in KHz. 173 174scaling_min_freq and 175scaling_max_freq show the current "policy limits" (in 176 kHz). By echoing new values into these 177 files, you can change these limits. 178 NOTE: when setting a policy you need to 179 first set scaling_max_freq, then 180 scaling_min_freq. 181 182affected_cpus : List of CPUs that require software coordination 183 of frequency. 184 185related_cpus : List of CPUs that need some sort of frequency 186 coordination, whether software or hardware. 187 188scaling_driver : Hardware driver for cpufreq. 189 190scaling_cur_freq : Current frequency of the CPU, in KHz. 191 192If you have selected the "userspace" governor which allows you to 193set the CPU operating frequency to a specific value, you can read out 194the current frequency in 195 196scaling_setspeed. By "echoing" a new frequency into this 197 you can change the speed of the CPU, 198 but only within the limits of 199 scaling_min_freq and scaling_max_freq. 200 201 2023.2 Deprecated Interfaces 203------------------------- 204 205Depending on your kernel configuration, you might find the following 206cpufreq-related files: 207/proc/cpufreq 208/proc/sys/cpu/*/speed 209/proc/sys/cpu/*/speed-min 210/proc/sys/cpu/*/speed-max 211 212These are files for deprecated interfaces to cpufreq, which offer far 213less functionality. Because of this, these interfaces aren't described 214here. 215 216