redonkable
/
alistair23-linux
1
0
Fork 0
Code Releases Activity

Documentation: cpufreq / boost: Update BOOST documentation 

Since the support for software and hardware controlled boosting has
been added, update the corresponding documentation.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Myungjoo Ham <myungjoo.ham@samsung.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
hifive-unleashed-5.1
Lukasz Majewski 2013-12-20 15:24:53 +01:00 committed by Rafael J. Wysocki
parent c683c2c963
commit 0636f0c36a
1 changed files with 13 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
Documentation/cpu-freq/boost.txt
View File

@ -17,8 +17,8 @@ Introduction
Some CPUs support a functionality to raise the operating frequency of Some CPUs support a functionality to raise the operating frequency of
some cores in a multi-core package if certain conditions apply, mostly 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 if the whole chip is not fully utilized and below it's intended thermal
budget. This is done without operating system control by a combination budget. The decision about boost disable/enable is made either at hardware
of hardware and firmware. (e.g. x86) or software (e.g ARM).
On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core", On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core",
in technical documentation "Core performance boost". In Linux we use in technical documentation "Core performance boost". In Linux we use
the term "boost" for convenience. the term "boost" for convenience.
@ -48,24 +48,24 @@ be desirable:
User controlled switch User controlled switch
---------------------- ----------------------
To allow the user to toggle the boosting functionality, the acpi-cpufreq To allow the user to toggle the boosting functionality, the cpufreq core
driver exports a sysfs knob to disable it. There is a file: driver exports a sysfs knob to enable or disable it. There is a file:
/sys/devices/system/cpu/cpufreq/boost /sys/devices/system/cpu/cpufreq/boost
which can either read "0" (boosting disabled) or "1" (boosting enabled). which can either read "0" (boosting disabled) or "1" (boosting enabled).
Reading the file is always supported, even if the processor does not The file is exported only when cpufreq driver supports boosting.
support boosting. In this case the file will be read-only and always Explicitly changing the permissions and writing to that file anyway will
reads as "0". Explicitly changing the permissions and writing to that return EINVAL.
file anyway will return EINVAL.
On supported CPUs one can write either a "0" or a "1" into this file. 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 This will either disable the boost functionality on all cores in the
whole system (0) or will allow the hardware to boost at will (1). 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 Writing a "1" does not explicitly boost the system, but just allows the
CPU (and the firmware) to boost at their discretion. Some implementations CPU to boost at their discretion. Some implementations take external
take external factors like the chip's temperature into account, so factors like the chip's temperature into account, so boosting once does
boosting once does not necessarily mean that it will occur every time not necessarily mean that it will occur every time even using the exact
even using the exact same software setup. same software setup.
AMD legacy cpb switch AMD legacy cpb switch