[PATCH 1/1] Honor state disabling in the cpuidle ladder governor

From: Carsten Emde
Date: Tue Jul 17 2012 - 15:18:58 EST

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 <C.Emde@xxxxxxxxx>

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) {
@@ -100,7 +101,8 @@ static int ladder_select_state(struct cp

/* consider demotion */
- 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--) {

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