[PATCH 1/1 v3] Honor state disabling in the cpuidle ladder governor

From: Carsten Emde
Date: Thu Jul 19 2012 - 16:50:33 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.

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@xxxxxxxxx>

---
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 &&
+ !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 cp

/* 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--) {

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