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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>
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2 changed files with 12 additions and 2 deletions
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@ -76,9 +76,17 @@ total 0
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* desc : Small description about the idle state (string)
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* disable : Option to disable this idle state (bool)
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* disable : Option to disable this idle state (bool) -> see note below
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* latency : Latency to exit out of this idle state (in microseconds)
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* name : Name of the idle state (string)
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* power : Power consumed while in this idle state (in milliwatts)
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* time : Total time spent in this idle state (in microseconds)
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* usage : Number of times this state was entered (count)
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Note:
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The behavior and the effect of the disable variable depends on the
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implementation of a particular governor. In the ladder governor, for
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example, it is not coherent, i.e. if one is disabling a light state,
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then all deeper states are disabled as well, but the disable variable
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does not reflect it. Likewise, if one enables a deep state but a lighter
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state still is disabled, then this has no effect.
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@ -88,6 +88,7 @@ static int ladder_select_state(struct cpuidle_driver *drv,
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/* consider promotion */
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if (last_idx < drv->state_count - 1 &&
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!dev->states_usage[last_idx + 1].disable &&
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last_residency > last_state->threshold.promotion_time &&
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drv->states[last_idx + 1].exit_latency <= latency_req) {
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last_state->stats.promotion_count++;
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@ -100,7 +101,8 @@ static int ladder_select_state(struct cpuidle_driver *drv,
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/* consider demotion */
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if (last_idx > CPUIDLE_DRIVER_STATE_START &&
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drv->states[last_idx].exit_latency > latency_req) {
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(dev->states_usage[last_idx].disable ||
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drv->states[last_idx].exit_latency > latency_req)) {
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int i;
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for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {
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