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cpuidle: Quickly notice prediction failure in general case

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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: Rik van Riel <riel@redhat.com>
Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Youquan Song 2012-10-26 12:26:50 +02:00 committed by Rafael J. Wysocki
parent 69a37beabf
commit e11538d1f0
1 changed files with 33 additions and 1 deletions
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34
drivers/cpuidle/governors/menu.c
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@ -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;