Subject: Honor state disabling in the cpuidle ladder governor From: Carsten Emde Date: Tue, 17 Jul 2012 19:50:13 +0100 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 addded to the documentation. Signed-off-by: Carsten Emde --- Documentation/cpuidle/sysfs.txt | 10 +++++++++- drivers/cpuidle/governors/ladder.c | 4 +++- 2 files changed, 12 insertions(+), 2 deletions(-) Index: linux-3.4.4-rt14-rc2-64/Documentation/cpuidle/sysfs.txt =================================================================== --- linux-3.4.4-rt14-rc2-64.orig/Documentation/cpuidle/sysfs.txt +++ linux-3.4.4-rt14-rc2-64/Documentation/cpuidle/sysfs.txt @@ -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. Index: linux-3.4.4-rt14-rc2-64/drivers/cpuidle/governors/ladder.c =================================================================== --- linux-3.4.4-rt14-rc2-64.orig/drivers/cpuidle/governors/ladder.c +++ linux-3.4.4-rt14-rc2-64/drivers/cpuidle/governors/ladder.c @@ -88,6 +88,7 @@ static int ladder_select_state(struct cp /* consider promotion */ if (last_idx < drv->state_count - 1 && + !drv->states[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 cp /* consider demotion */ if (last_idx > CPUIDLE_DRIVER_STATE_START && - drv->states[last_idx].exit_latency > latency_req) { + (drv->states[last_idx].disable || + drv->states[last_idx].exit_latency > latency_req)) { int i; for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {