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authorLukasz Majewski <l.majewski@samsung.com>2013-12-20 09:24:53 -0500
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2014-01-16 20:00:45 -0500
commit0636f0c36a7f1fb4612f55f5fdffdcd12d8a4121 (patch)
tree2d713d87c6603c5032672b4bb98c6f82181e3f13
parentc683c2c96315d4bfed40f96d6fb3d35513f74632 (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.txt26
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
17Some CPUs support a functionality to raise the operating frequency of 17Some CPUs support a functionality to raise the operating frequency of
18some cores in a multi-core package if certain conditions apply, mostly 18some cores in a multi-core package if certain conditions apply, mostly
19if the whole chip is not fully utilized and below it's intended thermal 19if the whole chip is not fully utilized and below it's intended thermal
20budget. This is done without operating system control by a combination 20budget. The decision about boost disable/enable is made either at hardware
21of hardware and firmware. 21(e.g. x86) or software (e.g ARM).
22On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core", 22On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core",
23in technical documentation "Core performance boost". In Linux we use 23in technical documentation "Core performance boost". In Linux we use
24the term "boost" for convenience. 24the term "boost" for convenience.
@@ -48,24 +48,24 @@ be desirable:
48User controlled switch 48User controlled switch
49---------------------- 49----------------------
50 50
51To allow the user to toggle the boosting functionality, the acpi-cpufreq 51To allow the user to toggle the boosting functionality, the cpufreq core
52driver exports a sysfs knob to disable it. There is a file: 52driver 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
54which can either read "0" (boosting disabled) or "1" (boosting enabled). 54which can either read "0" (boosting disabled) or "1" (boosting enabled).
55Reading the file is always supported, even if the processor does not 55The file is exported only when cpufreq driver supports boosting.
56support boosting. In this case the file will be read-only and always 56Explicitly changing the permissions and writing to that file anyway will
57reads as "0". Explicitly changing the permissions and writing to that 57return EINVAL.
58file anyway will return EINVAL.
59 58
60On supported CPUs one can write either a "0" or a "1" into this file. 59On supported CPUs one can write either a "0" or a "1" into this file.
61This will either disable the boost functionality on all cores in the 60This will either disable the boost functionality on all cores in the
62whole system (0) or will allow the hardware to boost at will (1). 61whole system (0) or will allow the software or hardware to boost at will
62(1).
63 63
64Writing a "1" does not explicitly boost the system, but just allows the 64Writing a "1" does not explicitly boost the system, but just allows the
65CPU (and the firmware) to boost at their discretion. Some implementations 65CPU to boost at their discretion. Some implementations take external
66take external factors like the chip's temperature into account, so 66factors like the chip's temperature into account, so boosting once does
67boosting once does not necessarily mean that it will occur every time 67not necessarily mean that it will occur every time even using the exact
68even using the exact same software setup. 68same software setup.
69 69
70 70
71AMD legacy cpb switch 71AMD legacy cpb switch