diff options
author | Carsten Emde <C.Emde@osadl.org> | 2012-07-19 16:34:10 -0400 |
---|---|---|
committer | Rafael J. Wysocki <rjw@sisk.pl> | 2012-09-03 19:35:44 -0400 |
commit | 62d6ae880e3e76098d5e345decd2dce443975889 (patch) | |
tree | 5788868e10c08030c5981adae8f5dfd6306b2608 /Documentation/cpuidle | |
parent | 4cbe5a555fa58a79b6ecbb6c531b8bab0650778d (diff) |
Honor state disabling in the cpuidle ladder governor
There are two cpuidle governors ladder and menu. While the ladder
governor is always available, if CONFIG_CPU_IDLE is selected, the
menu governor additionally requires CONFIG_NO_HZ.
A particular C state can be disabled by writing to the sysfs file
/sys/devices/system/cpu/cpuN/cpuidle/stateN/disable, but this mechanism
is only implemented in the menu governor. Thus, in a system where
CONFIG_NO_HZ is not selected, the ladder governor becomes default and
always will walk through all sleep states - irrespective of whether the
C state was disabled via sysfs or not. The only way to select a specific
C state was to write the related latency to /dev/cpu_dma_latency and
keep the file open as long as this setting was required - not very
practical and not suitable for setting a single core in an SMP system.
With this patch, the ladder governor only will promote to the next
C state, if it has not been disabled, and it will demote, if the
current C state was disabled.
Note that the patch does not make the setting of the sysfs variable
"disable" coherent, i.e. if one is disabling a light state, then all
deeper states are disabled as well, but the "disable" variable does not
reflect it. Likewise, if one enables a deep state but a lighter state
still is disabled, then this has no effect. A related section has been
added to the documentation.
Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Diffstat (limited to 'Documentation/cpuidle')
-rw-r--r-- | Documentation/cpuidle/sysfs.txt | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/Documentation/cpuidle/sysfs.txt b/Documentation/cpuidle/sysfs.txt index 9d28a3406e74..b6f44f490ed7 100644 --- a/Documentation/cpuidle/sysfs.txt +++ b/Documentation/cpuidle/sysfs.txt | |||
@@ -76,9 +76,17 @@ total 0 | |||
76 | 76 | ||
77 | 77 | ||
78 | * desc : Small description about the idle state (string) | 78 | * desc : Small description about the idle state (string) |
79 | * disable : Option to disable this idle state (bool) | 79 | * disable : Option to disable this idle state (bool) -> see note below |
80 | * latency : Latency to exit out of this idle state (in microseconds) | 80 | * latency : Latency to exit out of this idle state (in microseconds) |
81 | * name : Name of the idle state (string) | 81 | * name : Name of the idle state (string) |
82 | * power : Power consumed while in this idle state (in milliwatts) | 82 | * power : Power consumed while in this idle state (in milliwatts) |
83 | * time : Total time spent in this idle state (in microseconds) | 83 | * time : Total time spent in this idle state (in microseconds) |
84 | * usage : Number of times this state was entered (count) | 84 | * usage : Number of times this state was entered (count) |
85 | |||
86 | Note: | ||
87 | The behavior and the effect of the disable variable depends on the | ||
88 | implementation of a particular governor. In the ladder governor, for | ||
89 | example, it is not coherent, i.e. if one is disabling a light state, | ||
90 | then all deeper states are disabled as well, but the disable variable | ||
91 | does not reflect it. Likewise, if one enables a deep state but a lighter | ||
92 | state still is disabled, then this has no effect. | ||