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>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
index b6a09ea859b1..2aef26c520bb 100644
--- a/drivers/cpuidle/governors/ladder.c
+++ b/drivers/cpuidle/governors/ladder.c
@@ -88,6 +88,7 @@ static int ladder_select_state(struct cpuidle_driver *drv,
 
         /* consider promotion */
         if (last_idx < drv->state_count - 1 &&
+            !dev->states_usage[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 cpuidle_driver *drv,
 
         /* consider demotion */
         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;
 
                 for (i = last_idx - 1; i > CPUIDLE_DRIVER_STATE_START; i--) {