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. Signed-off-by: Carsten Emde --- drivers/cpuidle/governors/ladder.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) 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--) { -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/