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Diffstat (limited to 'Documentation/cpu-freq/boost.txt')
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diff --git a/Documentation/cpu-freq/boost.txt b/Documentation/cpu-freq/boost.txt deleted file mode 100644 index dd62e1334f0a..000000000000 --- a/Documentation/cpu-freq/boost.txt +++ /dev/null @@ -1,93 +0,0 @@ -Processor boosting control - - - information for users - - -Quick guide for the impatient: --------------------- -/sys/devices/system/cpu/cpufreq/boost -controls the boost setting for the whole system. You can read and write -that file with either "0" (boosting disabled) or "1" (boosting allowed). -Reading or writing 1 does not mean that the system is boosting at this -very moment, but only that the CPU _may_ raise the frequency at it's -discretion. --------------------- - -Introduction -------------- -Some CPUs support a functionality to raise the operating frequency of -some cores in a multi-core package if certain conditions apply, mostly -if the whole chip is not fully utilized and below it's intended thermal -budget. The decision about boost disable/enable is made either at hardware -(e.g. x86) or software (e.g ARM). -On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core", -in technical documentation "Core performance boost". In Linux we use -the term "boost" for convenience. - -Rationale for disable switch ----------------------------- - -Though the idea is to just give better performance without any user -intervention, sometimes the need arises to disable this functionality. -Most systems offer a switch in the (BIOS) firmware to disable the -functionality at all, but a more fine-grained and dynamic control would -be desirable: -1. While running benchmarks, reproducible results are important. Since - the boosting functionality depends on the load of the whole package, - single thread performance can vary. By explicitly disabling the boost - functionality at least for the benchmark's run-time the system will run - at a fixed frequency and results are reproducible again. -2. To examine the impact of the boosting functionality it is helpful - to do tests with and without boosting. -3. Boosting means overclocking the processor, though under controlled - conditions. By raising the frequency and the voltage the processor - will consume more power than without the boosting, which may be - undesirable for instance for mobile users. Disabling boosting may - save power here, though this depends on the workload. - - -User controlled switch ----------------------- - -To allow the user to toggle the boosting functionality, the cpufreq core -driver exports a sysfs knob to enable or disable it. There is a file: -/sys/devices/system/cpu/cpufreq/boost -which can either read "0" (boosting disabled) or "1" (boosting enabled). -The file is exported only when cpufreq driver supports boosting. -Explicitly changing the permissions and writing to that file anyway will -return EINVAL. - -On supported CPUs one can write either a "0" or a "1" into this file. -This will either disable the boost functionality on all cores in the -whole system (0) or will allow the software or hardware to boost at will -(1). - -Writing a "1" does not explicitly boost the system, but just allows the -CPU to boost at their discretion. Some implementations take external -factors like the chip's temperature into account, so boosting once does -not necessarily mean that it will occur every time even using the exact -same software setup. - - -AMD legacy cpb switch ---------------------- -The AMD powernow-k8 driver used to support a very similar switch to -disable or enable the "Core Performance Boost" feature of some AMD CPUs. -This switch was instantiated in each CPU's cpufreq directory -(/sys/devices/system/cpu[0-9]*/cpufreq) and was called "cpb". -Though the per CPU existence hints at a more fine grained control, the -actual implementation only supported a system-global switch semantics, -which was simply reflected into each CPU's file. Writing a 0 or 1 into it -would pull the other CPUs to the same state. -For compatibility reasons this file and its behavior is still supported -on AMD CPUs, though it is now protected by a config switch -(X86_ACPI_CPUFREQ_CPB). On Intel CPUs this file will never be created, -even with the config option set. -This functionality is considered legacy and will be removed in some future -kernel version. - -More fine grained boosting control ----------------------------------- - -Technically it is possible to switch the boosting functionality at least -on a per package basis, for some CPUs even per core. Currently the driver -does not support it, but this may be implemented in the future. |