cpuidle: add a sysfs entry to disable specific C state for debug purpose.

Some C states of new CPU might be not good.  One reason is BIOS might
configure them incorrectly.  To help developers root cause it quickly, the
patch adds a new sysfs entry, so developers could disable specific C state
manually.

In addition, C state might have much impact on performance tuning, as it
takes much time to enter/exit C states, which might delay interrupt
processing.  With the new debug option, developers could check if a deep C
state could impact performance and how much impact it could cause.

Also add this option in Documentation/cpuidle/sysfs.txt.

[akpm@linux-foundation.org: check kstrtol return value]
Signed-off-by: ShuoX Liu <shuox.liu@intel.com>
Reviewed-by: Yanmin Zhang <yanmin_zhang@intel.com>
Reviewed-and-Tested-by: Deepthi Dharwar <deepthi@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index ad0952601ae2..5c17ca112fc2 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -280,7 +280,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
          * We want to default to C1 (hlt), not to busy polling
          * unless the timer is happening really really soon.
          */
-        if (data->expected_us > 5)
+        if (data->expected_us > 5 &&
+                drv->states[CPUIDLE_DRIVER_STATE_START].disable == 0)
                 data->last_state_idx = CPUIDLE_DRIVER_STATE_START;
 
         /*
@@ -290,6 +291,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
         for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
                 struct cpuidle_state *s = &drv->states[i];
 
+                if (s->disable)
+                        continue;
                 if (s->target_residency > data->predicted_us)
                         continue;
                 if (s->exit_latency > latency_req)