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[PATCH 2/3] x86,idle: Quickly notice prediction failure in general case

 

 

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youquan.song at intel

May 10, 2012, 8:20 PM

Post #1 of 1 (66 views)
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[PATCH 2/3] x86,idle: Quickly notice prediction failure in general case

The patch extends the patch to enhance the prediction for repeat mode by add a
timer when menu governor choose a shallow C-state.
The timer is set to time out in 50 milli-seconds by default. It is special twist
that there are no power saving gains even sleep longer than it.

When C-state is waken up prior to the adding timer, the timer will be cancelled
initiatively. When the timer is triggered and menu governor will quickly notice
prediction failure and re-evaluates deeper C-states possibility.

Signed-off-by: Youquan Song <youquan.song [at] intel>
---
drivers/cpuidle/governors/menu.c | 48 ++++++++++++++++++++++++++------------
1 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 8c23fbd..9f92dd4 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -113,6 +113,13 @@ static DEFINE_PER_CPU(int, hrtimer_started);
* represented in the system load average.
*
*/
+
+/*
+ * Default set to 50 milliseconds based on special twist mentioned above that
+ * there are no power gains sleep longer than it.
+ */
+static unsigned int perfect_cstate_ms __read_mostly = 50;
+module_param(perfect_cstate_ms, uint, 0000);

struct menu_device {
int last_state_idx;
@@ -343,26 +350,37 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
data->exit_us = s->exit_latency;
}
}
-
+
+ /* not deepest C-state chosen */
if (data->last_state_idx < drv->state_count - 1) {
+ unsigned int repeat_us = 0;
+ unsigned int perfect_us = 0;
+
+ /*
+ * Set enough timer to recognize the repeat mode broken.
+ * If the timer is time out, the repeat mode prediction
+ * fails,then re-evaluate deeper C-states possibility.
+ * If the timer is not triggered, the timer will be
+ * cancelled when CPU waken up.
+ */
+ repeat_us =
+ (repeat ? (2 * data->predicted_us + MAX_DEVIATION) : 0);
+ perfect_us = perfect_cstate_ms * 1000;

/* Repeat mode detected */
- if (repeat) {
- unsigned int repeat_us = 0;
- /*
- * Set enough timer to recognize the repeat mode broken.
- * If the timer is time out, the repeat mode prediction
- * fails,then re-evaluate deeper C-states possibility.
- * If the timer is not triggered, the timer will be
- * cancelled when CPU waken up.
- */
- repeat_us = 2 * data->predicted_us + MAX_DEVIATION;
- hrtimer_start(hrtmr, ns_to_ktime(1000 * repeat_us),
- HRTIMER_MODE_REL_PINNED);
+ if (repeat && (repeat_us < perfect_us)) {
+ hrtimer_start(hrtmr, ns_to_ktime(1000 * repeat_us),
+ HRTIMER_MODE_REL_PINNED);
+ /* menu hrtimer is started */
+ per_cpu(hrtimer_started, cpu) = 1;
+ } else if (perfect_us < data->expected_us) {
+ /* expected time is larger than adding timer time */
+ hrtimer_start(hrtmr, ns_to_ktime(1000 * perfect_us),
+ HRTIMER_MODE_REL_PINNED);
/* menu hrtimer is started */
per_cpu(hrtimer_started, cpu) = 1;
- }
- }
+ }
+ }

return data->last_state_idx;
}
--
1.6.4.2

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