Commit 62d6ae88 authored by Carsten Emde's avatar Carsten Emde Committed by Rafael J. Wysocki

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
...@@ -76,9 +76,17 @@ total 0 ...@@ -76,9 +76,17 @@ total 0
* desc : Small description about the idle state (string) * 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) * latency : Latency to exit out of this idle state (in microseconds)
* name : Name of the idle state (string) * name : Name of the idle state (string)
* power : Power consumed while in this idle state (in milliwatts) * power : Power consumed while in this idle state (in milliwatts)
* time : Total time spent in this idle state (in microseconds) * time : Total time spent in this idle state (in microseconds)
* usage : Number of times this state was entered (count) * 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.
...@@ -88,6 +88,7 @@ static int ladder_select_state(struct cpuidle_driver *drv, ...@@ -88,6 +88,7 @@ static int ladder_select_state(struct cpuidle_driver *drv,
/* consider promotion */ /* consider promotion */
if (last_idx < drv->state_count - 1 && if (last_idx < drv->state_count - 1 &&
!dev->states_usage[last_idx + 1].disable &&
last_residency > last_state->threshold.promotion_time && last_residency > last_state->threshold.promotion_time &&
drv->states[last_idx + 1].exit_latency <= latency_req) { drv->states[last_idx + 1].exit_latency <= latency_req) {
last_state->stats.promotion_count++; last_state->stats.promotion_count++;
...@@ -100,7 +101,8 @@ static int ladder_select_state(struct cpuidle_driver *drv, ...@@ -100,7 +101,8 @@ static int ladder_select_state(struct cpuidle_driver *drv,
/* consider demotion */ /* consider demotion */
if (last_idx > CPUIDLE_DRIVER_STATE_START && 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; int i;
for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) { for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
......
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