diff options
| author | Lukasz Majewski <l.majewski@samsung.com> | 2013-12-20 15:24:53 +0100 |
|---|---|---|
| committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2014-01-17 02:00:45 +0100 |
| commit | 0636f0c36a7f1fb4612f55f5fdffdcd12d8a4121 (patch) | |
| tree | 2d713d87c6603c5032672b4bb98c6f82181e3f13 /Documentation/cpu-freq | |
| parent | c683c2c96315d4bfed40f96d6fb3d35513f74632 (diff) | |
| download | lwn-0636f0c36a7f1fb4612f55f5fdffdcd12d8a4121.tar.gz lwn-0636f0c36a7f1fb4612f55f5fdffdcd12d8a4121.zip | |
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>
Diffstat (limited to 'Documentation/cpu-freq')
| -rw-r--r-- | Documentation/cpu-freq/boost.txt | 26 |
1 files changed, 13 insertions, 13 deletions
diff --git a/Documentation/cpu-freq/boost.txt b/Documentation/cpu-freq/boost.txt index 9b4edfcf486f..dd62e1334f0a 100644 --- a/Documentation/cpu-freq/boost.txt +++ b/Documentation/cpu-freq/boost.txt @@ -17,8 +17,8 @@ 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. This is done without operating system control by a combination -of hardware and firmware. +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. @@ -48,24 +48,24 @@ be desirable: User controlled switch ---------------------- -To allow the user to toggle the boosting functionality, the acpi-cpufreq -driver exports a sysfs knob to disable it. There is a file: +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). -Reading the file is always supported, even if the processor does not -support boosting. In this case the file will be read-only and always -reads as "0". Explicitly changing the permissions and writing to that -file anyway will return EINVAL. +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 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 -CPU (and the firmware) 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. +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 |