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Commit 62d6ae88 authored by Carsten Emde's avatar Carsten Emde Committed by Rafael J. Wysocki
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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: default avatarCarsten Emde <C.Emde@osadl.org>
Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
parent 4cbe5a55

Documentation/cpuidle/sysfs.txt

+9 −1
Original line number Diff line number Diff line
@@ -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.

drivers/cpuidle/governors/ladder.c

+3 −1
Original line number Diff line number Diff line
@@ -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--) {