diff mbox

[37/94] cpuidle: Add decaying history logic to menu idle predictor

Message ID 816bb611e41be29b476dc16f6297eb551bf4d747.1231492609.git.len.brown@intel.com (mailing list archive)
State Accepted, archived
Headers show

Commit Message

Len Brown Jan. 9, 2009, 9:26 a.m. UTC 
From: Pallipadi, Venkatesh <venkatesh.pallipadi@intel.com>

Add decaying history of predicted idle time, instead of using the last early
wakeup. This logic helps menu governor do better job of predicting idle time.

With this change, we also measured noticable (~8%) power savings on
a DP server system with CPUs supporting deep C states, when system
was lightly loaded. There was no change to power or perf on other load
conditions.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
---
 drivers/cpuidle/governors/menu.c |   10 +++++++++-
 1 files changed, 9 insertions(+), 1 deletions(-)
diff mbox

Patch

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 8d7cf3f..f1df59f 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -15,12 +15,14 @@ 
 #include <linux/tick.h>
 
 #define BREAK_FUZZ	4	/* 4 us */
+#define PRED_HISTORY_PCT	50
 
 struct menu_device {
 	int		last_state_idx;
 
 	unsigned int	expected_us;
 	unsigned int	predicted_us;
+	unsigned int    current_predicted_us;
 	unsigned int	last_measured_us;
 	unsigned int	elapsed_us;
 };
@@ -47,6 +49,12 @@  static int menu_select(struct cpuidle_device *dev)
 	data->expected_us =
 		(u32) ktime_to_ns(tick_nohz_get_sleep_length()) / 1000;
 
+	/* Recalculate predicted_us based on prediction_history_pct */
+	data->predicted_us *= PRED_HISTORY_PCT;
+	data->predicted_us += (100 - PRED_HISTORY_PCT) *
+				data->current_predicted_us;
+	data->predicted_us /= 100;
+
 	/* find the deepest idle state that satisfies our constraints */
 	for (i = CPUIDLE_DRIVER_STATE_START + 1; i < dev->state_count; i++) {
 		struct cpuidle_state *s = &dev->states[i];
@@ -97,7 +105,7 @@  static void menu_reflect(struct cpuidle_device *dev)
 		measured_us = -1;
 
 	/* Predict time until next break event */
-	data->predicted_us = max(measured_us, data->last_measured_us);
+	data->current_predicted_us = max(measured_us, data->last_measured_us);
 
 	if (last_idle_us + BREAK_FUZZ <
 	    data->expected_us - target->exit_latency) {