|author||Lukasz Majewski <email@example.com>||2013-12-20 15:24:53 +0100|
|committer||Rafael J. Wysocki <firstname.lastname@example.org>||2014-01-17 02:00:45 +0100|
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 <email@example.com> Signed-off-by: Myungjoo Ham <firstname.lastname@example.org> Acked-by: Viresh Kumar <email@example.com> Signed-off-by: Rafael J. Wysocki <firstname.lastname@example.org>
Diffstat (limited to 'Documentation/cpu-freq')
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
@@ -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:
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
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
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