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Commit e11538d1 authored by Youquan Song's avatar Youquan Song Committed by Rafael J. Wysocki
Browse files

cpuidle: Quickly notice prediction failure in general case 



The prediction for future is difficult and when the cpuidle governor prediction
fails and govenor possibly choose the shallower C-state than it should. How to
quickly notice and find the failure becomes important for power saving.

The patch extends to general case that prediction logic get a small predicted
residency, so it choose a shallow C-state though the expected residency is large
. Once the prediction will be fail, the CPU will keep staying at shallow C-state
for a long time. Acutally, the CPU has change enter into deep C-state.
So when the expected residency is long enough but governor choose a shallow
C-state, an timer will be added in order to monitor if the prediction failure.

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: default avatarRik van Riel <riel@redhat.com>
Signed-off-by: default avatarYouquan Song <youquan.song@intel.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 69a37bea

drivers/cpuidle/governors/menu.c

+33 −1
Original line number Diff line number Diff line
@@ -34,7 +34,7 @@ 
static DEFINE_PER_CPU(struct hrtimer, menu_hrtimer);

static DEFINE_PER_CPU(int, hrtimer_status);

/* menu hrtimer mode */

enum {MENU_HRTIMER_STOP, MENU_HRTIMER_REPEAT};

enum {MENU_HRTIMER_STOP, MENU_HRTIMER_REPEAT, MENU_HRTIMER_GENERAL};



/*

 * Concepts and ideas behind the menu governor
@@ -116,6 +116,13 @@ enum {MENU_HRTIMER_STOP, MENU_HRTIMER_REPEAT}; 
 *

 */



/*

 * The C-state residency is so long that is is worthwhile to exit

 * from the shallow C-state and re-enter into a deeper C-state.

 */

static unsigned int perfect_cstate_ms __read_mostly = 30;

module_param(perfect_cstate_ms, uint, 0000);



struct menu_device {

	int		last_state_idx;

	int             needs_update;
@@ -216,6 +223,16 @@ EXPORT_SYMBOL_GPL(menu_hrtimer_cancel); 
static enum hrtimer_restart menu_hrtimer_notify(struct hrtimer *hrtimer)

{

	int cpu = smp_processor_id();

	struct menu_device *data = &per_cpu(menu_devices, cpu);



	/* In general case, the expected residency is much larger than

	 *  deepest C-state target residency, but prediction logic still

	 *  predicts a small predicted residency, so the prediction

	 *  history is totally broken if the timer is triggered.

	 *  So reset the correction factor.

	 */

	if (per_cpu(hrtimer_status, cpu) == MENU_HRTIMER_GENERAL)

		data->correction_factor[data->bucket] = RESOLUTION * DECAY;



	per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_STOP;
@@ -353,6 +370,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) 
	/* not deepest C-state chosen for low predicted residency */

	if (low_predicted) {

		unsigned int timer_us = 0;

		unsigned int perfect_us = 0;



		/*

		 * Set a timer to detect whether this sleep is much
@@ -363,12 +381,26 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev) 
		 */

		timer_us = 2 * (data->predicted_us + MAX_DEVIATION);



		perfect_us = perfect_cstate_ms * 1000;



		if (repeat && (4 * timer_us < data->expected_us)) {

			hrtimer_start(hrtmr, ns_to_ktime(1000 * timer_us),

				HRTIMER_MODE_REL_PINNED);

			/* In repeat case, menu hrtimer is started */

			per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_REPEAT;

		} else if (perfect_us < data->expected_us) {

			/*

			 * The next timer is long. This could be because

			 * we did not make a useful prediction.

			 * In that case, it makes sense to re-enter

			 * into a deeper C-state after some time.

			 */

			hrtimer_start(hrtmr, ns_to_ktime(1000 * timer_us),

				HRTIMER_MODE_REL_PINNED);

			/* In general case, menu hrtimer is started */

			per_cpu(hrtimer_status, cpu) = MENU_HRTIMER_GENERAL;

		}



	}



	return data->last_state_idx;