diff options
author | Lukasz Majewski <l.majewski@samsung.com> | 2013-12-20 09:24:53 -0500 |
---|---|---|
committer | Rafael J. Wysocki <rafael.j.wysocki@intel.com> | 2014-01-16 20:00:45 -0500 |
commit | 0636f0c36a7f1fb4612f55f5fdffdcd12d8a4121 (patch) | |
tree | 2d713d87c6603c5032672b4bb98c6f82181e3f13 | |
parent | c683c2c96315d4bfed40f96d6fb3d35513f74632 (diff) |
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>
-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 | |||
17 | Some CPUs support a functionality to raise the operating frequency of | 17 | Some CPUs support a functionality to raise the operating frequency of |
18 | some cores in a multi-core package if certain conditions apply, mostly | 18 | some cores in a multi-core package if certain conditions apply, mostly |
19 | if the whole chip is not fully utilized and below it's intended thermal | 19 | if the whole chip is not fully utilized and below it's intended thermal |
20 | budget. This is done without operating system control by a combination | 20 | budget. The decision about boost disable/enable is made either at hardware |
21 | of hardware and firmware. | 21 | (e.g. x86) or software (e.g ARM). |
22 | On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core", | 22 | On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core", |
23 | in technical documentation "Core performance boost". In Linux we use | 23 | in technical documentation "Core performance boost". In Linux we use |
24 | the term "boost" for convenience. | 24 | the term "boost" for convenience. |
@@ -48,24 +48,24 @@ be desirable: | |||
48 | User controlled switch | 48 | User controlled switch |
49 | ---------------------- | 49 | ---------------------- |
50 | 50 | ||
51 | To allow the user to toggle the boosting functionality, the acpi-cpufreq | 51 | To allow the user to toggle the boosting functionality, the cpufreq core |
52 | driver exports a sysfs knob to disable it. There is a file: | 52 | driver exports a sysfs knob to enable or disable it. There is a file: |
53 | /sys/devices/system/cpu/cpufreq/boost | 53 | /sys/devices/system/cpu/cpufreq/boost |
54 | which can either read "0" (boosting disabled) or "1" (boosting enabled). | 54 | which can either read "0" (boosting disabled) or "1" (boosting enabled). |
55 | Reading the file is always supported, even if the processor does not | 55 | The file is exported only when cpufreq driver supports boosting. |
56 | support boosting. In this case the file will be read-only and always | 56 | Explicitly changing the permissions and writing to that file anyway will |
57 | reads as "0". Explicitly changing the permissions and writing to that | 57 | return EINVAL. |
58 | file anyway will return EINVAL. | ||
59 | 58 | ||
60 | On supported CPUs one can write either a "0" or a "1" into this file. | 59 | On supported CPUs one can write either a "0" or a "1" into this file. |
61 | This will either disable the boost functionality on all cores in the | 60 | This will either disable the boost functionality on all cores in the |
62 | whole system (0) or will allow the hardware to boost at will (1). | 61 | whole system (0) or will allow the software or hardware to boost at will |
62 | (1). | ||
63 | 63 | ||
64 | Writing a "1" does not explicitly boost the system, but just allows the | 64 | Writing a "1" does not explicitly boost the system, but just allows the |
65 | CPU (and the firmware) to boost at their discretion. Some implementations | 65 | CPU to boost at their discretion. Some implementations take external |
66 | take external factors like the chip's temperature into account, so | 66 | factors like the chip's temperature into account, so boosting once does |
67 | boosting once does not necessarily mean that it will occur every time | 67 | not necessarily mean that it will occur every time even using the exact |
68 | even using the exact same software setup. | 68 | same software setup. |
69 | 69 | ||
70 | 70 | ||
71 | AMD legacy cpb switch | 71 | AMD legacy cpb switch |