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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>
This commit is contained in:
Carsten Emde 2012-07-19 20:34:10 +00:00 committed by Rafael J. Wysocki
parent 4cbe5a555f
commit 62d6ae880e
2 changed files with 12 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
Documentation/cpuidle/sysfs.txt
View File

@ -76,9 +76,17 @@ total 0
* desc : Small description about the idle state (string)
* disable : Option to disable this idle state (bool)
* disable : Option to disable this idle state (bool) -> see note below
* latency : Latency to exit out of this idle state (in microseconds)
* name : Name of the idle state (string)
* power : Power consumed while in this idle state (in milliwatts)
* time : Total time spent in this idle state (in microseconds)
* usage : Number of times this state was entered (count)
Note:
The behavior and the effect of the disable variable depends on the
implementation of a particular governor. In the ladder governor, for
example, it is not 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.

4
drivers/cpuidle/governors/ladder.c
View File

@ -88,6 +88,7 @@ static int ladder_select_state(struct cpuidle_driver *drv,
/* consider promotion */
if (last_idx < drv->state_count - 1 &&
!dev->states_usage[last_idx + 1].disable &&
last_residency > last_state->threshold.promotion_time &&
drv->states[last_idx + 1].exit_latency <= latency_req) {
last_state->stats.promotion_count++;
@ -100,7 +101,8 @@ static int ladder_select_state(struct cpuidle_driver *drv,
/* consider demotion */
if (last_idx > CPUIDLE_DRIVER_STATE_START &&
drv->states[last_idx].exit_latency > latency_req) {
(dev->states_usage[last_idx].disable ||
drv->states[last_idx].exit_latency > latency_req)) {
int i;
for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {