PM-runtime: Switch autosuspend over to using hrtimers

PM-runtime uses the timer infrastructure for autosuspend. This implies
that the minimum time before autosuspending a device is in the range
of 1 tick included to 2 ticks excluded
 -On arm64 this means between 4ms and 8ms with default jiffies
  configuration
 -And on arm, it is between 10ms and 20ms

These values are quite high for embedded systems which sometimes want
the duration to be in the range of 1 ms.

It is possible to switch autosuspend over to using hrtimers to get
finer granularity for short durations and take advantage of slack to
retain some margins and get long timeouts with minimum wakeups.

On an arm64 platform that uses 1ms for autosuspending timeout of its
GPU, idle power is reduced by 10% with hrtimer.

The latency impact on arm64 hikey octo cores is:
 - mark_last_busy: from 1.11 us to 1.25 us
 - rpm_suspend: from 15.54 us to 15.38 us
[Only the code path of rpm_suspend() that starts hrtimer has been
measured.]

arm64 image (arm64 default defconfig) decreases by around 3KB
with following details:

$ size vmlinux-timer
   text	   data	    bss	    dec	    hex	filename
12034646	6869268	 386840	19290754	1265a82	vmlinux

$ size vmlinux-hrtimer
   text	   data	    bss	    dec	    hex	filename
12030550	6870164	 387032	19287746	1264ec2	vmlinux

The latency impact on arm 32bits snowball dual cores is :
 - mark_last_busy: from 0.31 us usec to 0.77 us
 - rpm_suspend: from 6.83 us to 6.67 usec

The increase of the image for snowball platform that I used for
testing performance impact, is neglictable (244B).

$ size vmlinux-timer
   text	   data	    bss	    dec	    hex	filename
7157961	2119580	 264120	9541661	 91981d	build-ux500/vmlinux

size vmlinux-hrtimer
   text	   data	    bss	    dec	    hex	filename
7157773	21198846	 264248	9541905	 919911	vmlinux-hrtimer

And arm 32bits image (multi_v7_defconfig) increases by around 1.7KB
with following details:

$ size vmlinux-timer
   text	   data	    bss	    dec	    hex	filename
13304443	6803420	 402768	20510631	138f7a7	vmlinux

$ size vmlinux-hrtimer
   text	   data	    bss	    dec	    hex	filename
13304299	6805276	 402768	20512343	138fe57	vmlinux
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/base/power/runtime.c

@@ -8,6 +8,8 @@
  */
 
 #include <linux/sched/mm.h>
+#include <linux/ktime.h>
+#include <linux/hrtimer.h>
 #include <linux/export.h>
 #include <linux/pm_runtime.h>
 #include <linux/pm_wakeirq.h>
@@ -93,7 +95,7 @@ static void __update_runtime_status(struct device *dev, enum rpm_status status)
 static void pm_runtime_deactivate_timer(struct device *dev)
 {
 	if (dev->power.timer_expires > 0) {
-		del_timer(&dev->power.suspend_timer);
+		hrtimer_cancel(&dev->power.suspend_timer);
 		dev->power.timer_expires = 0;
 	}
 }
@@ -124,12 +126,11 @@ static void pm_runtime_cancel_pending(struct device *dev)
  * This function may be called either with or without dev->power.lock held.
  * Either way it can be racy, since power.last_busy may be updated at any time.
  */
-unsigned long pm_runtime_autosuspend_expiration(struct device *dev)
+u64 pm_runtime_autosuspend_expiration(struct device *dev)
 {
 	int autosuspend_delay;
-	long elapsed;
-	unsigned long last_busy;
-	unsigned long expires = 0;
+	u64 last_busy, expires = 0;
+	u64 now = ktime_to_ns(ktime_get());
 
 	if (!dev->power.use_autosuspend)
 		goto out;
@@ -139,19 +140,9 @@ unsigned long pm_runtime_autosuspend_expiration(struct device *dev)
 		goto out;
 
 	last_busy = READ_ONCE(dev->power.last_busy);
-	elapsed = jiffies - last_busy;
-	if (elapsed < 0)
-		goto out;	/* jiffies has wrapped around. */
 
-	/*
-	 * If the autosuspend_delay is >= 1 second, align the timer by rounding
-	 * up to the nearest second.
-	 */
-	expires = last_busy + msecs_to_jiffies(autosuspend_delay);
-	if (autosuspend_delay >= 1000)
-		expires = round_jiffies(expires);
-	expires += !expires;
-	if (elapsed >= expires - last_busy)
+	expires = last_busy + autosuspend_delay * NSEC_PER_MSEC;
+	if (expires <= now)
 		expires = 0;	/* Already expired. */
 
  out:
@@ -515,7 +506,7 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 	/* If the autosuspend_delay time hasn't expired yet, reschedule. */
 	if ((rpmflags & RPM_AUTO)
 	    && dev->power.runtime_status != RPM_SUSPENDING) {
-		unsigned long expires = pm_runtime_autosuspend_expiration(dev);
+		u64 expires = pm_runtime_autosuspend_expiration(dev);
 
 		if (expires != 0) {
 			/* Pending requests need to be canceled. */
@@ -528,10 +519,20 @@ static int rpm_suspend(struct device *dev, int rpmflags)
 			 * expire; pm_suspend_timer_fn() will take care of the
 			 * rest.
 			 */
-			if (!(dev->power.timer_expires && time_before_eq(
-			    dev->power.timer_expires, expires))) {
+			if (!(dev->power.timer_expires &&
+					dev->power.timer_expires <= expires)) {
+				/*
+				 * We add a slack of 25% to gather wakeups
+				 * without sacrificing the granularity.
+				 */
+				u64 slack = READ_ONCE(dev->power.autosuspend_delay) *
+						    (NSEC_PER_MSEC >> 2);
+
 				dev->power.timer_expires = expires;
-				mod_timer(&dev->power.suspend_timer, expires);
+				hrtimer_start_range_ns(&dev->power.suspend_timer,
+						ns_to_ktime(expires),
+						slack,
+						HRTIMER_MODE_ABS);
 			}
 			dev->power.timer_autosuspends = 1;
 			goto out;
@@ -895,23 +896,25 @@ static void pm_runtime_work(struct work_struct *work)
  *
  * Check if the time is right and queue a suspend request.
  */
-static void pm_suspend_timer_fn(struct timer_list *t)
+static enum hrtimer_restart  pm_suspend_timer_fn(struct hrtimer *timer)
 {
-	struct device *dev = from_timer(dev, t, power.suspend_timer);
+	struct device *dev = container_of(timer, struct device, power.suspend_timer);
 	unsigned long flags;
-	unsigned long expires;
+	u64 expires;
 
 	spin_lock_irqsave(&dev->power.lock, flags);
 
 	expires = dev->power.timer_expires;
 	/* If 'expire' is after 'jiffies' we've been called too early. */
-	if (expires > 0 && !time_after(expires, jiffies)) {
+	if (expires > 0 && expires < ktime_to_ns(ktime_get())) {
 		dev->power.timer_expires = 0;
 		rpm_suspend(dev, dev->power.timer_autosuspends ?
 		    (RPM_ASYNC | RPM_AUTO) : RPM_ASYNC);
 	}
 
 	spin_unlock_irqrestore(&dev->power.lock, flags);
+
+	return HRTIMER_NORESTART;
 }
 
 /**
@@ -922,6 +925,7 @@ static void pm_suspend_timer_fn(struct timer_list *t)
 int pm_schedule_suspend(struct device *dev, unsigned int delay)
 {
 	unsigned long flags;
+	ktime_t expires;
 	int retval;
 
 	spin_lock_irqsave(&dev->power.lock, flags);
@@ -938,10 +942,10 @@ int pm_schedule_suspend(struct device *dev, unsigned int delay)
 	/* Other scheduled or pending requests need to be canceled. */
 	pm_runtime_cancel_pending(dev);
 
-	dev->power.timer_expires = jiffies + msecs_to_jiffies(delay);
-	dev->power.timer_expires += !dev->power.timer_expires;
+	expires = ktime_add(ktime_get(), ms_to_ktime(delay));
+	dev->power.timer_expires = ktime_to_ns(expires);
 	dev->power.timer_autosuspends = 0;
-	mod_timer(&dev->power.suspend_timer, dev->power.timer_expires);
+	hrtimer_start(&dev->power.suspend_timer, expires, HRTIMER_MODE_ABS);
 
  out:
 	spin_unlock_irqrestore(&dev->power.lock, flags);
@@ -1491,7 +1495,8 @@ void pm_runtime_init(struct device *dev)
 	INIT_WORK(&dev->power.work, pm_runtime_work);
 
 	dev->power.timer_expires = 0;
-	timer_setup(&dev->power.suspend_timer, pm_suspend_timer_fn, 0);
+	hrtimer_init(&dev->power.suspend_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	dev->power.suspend_timer.function = pm_suspend_timer_fn;
 
 	init_waitqueue_head(&dev->power.wait_queue);
 }

include/linux/pm.h

@@ -26,6 +26,7 @@
 #include <linux/spinlock.h>
 #include <linux/wait.h>
 #include <linux/timer.h>
+#include <linux/hrtimer.h>
 #include <linux/completion.h>
 
 /*
@@ -608,7 +609,7 @@ struct dev_pm_info {
 	unsigned int		should_wakeup:1;
 #endif
 #ifdef CONFIG_PM
-	struct timer_list	suspend_timer;
+	struct hrtimer		suspend_timer;
 	unsigned long		timer_expires;
 	struct work_struct	work;
 	wait_queue_head_t	wait_queue;
@@ -631,7 +632,7 @@ struct dev_pm_info {
 	enum rpm_status		runtime_status;
 	int			runtime_error;
 	int			autosuspend_delay;
-	unsigned long		last_busy;
+	u64			last_busy;
 	unsigned long		active_jiffies;
 	unsigned long		suspended_jiffies;
 	unsigned long		accounting_timestamp;

include/linux/pm_runtime.h

@@ -51,7 +51,7 @@ extern void pm_runtime_no_callbacks(struct device *dev);
 extern void pm_runtime_irq_safe(struct device *dev);
 extern void __pm_runtime_use_autosuspend(struct device *dev, bool use);
 extern void pm_runtime_set_autosuspend_delay(struct device *dev, int delay);
-extern unsigned long pm_runtime_autosuspend_expiration(struct device *dev);
+extern u64 pm_runtime_autosuspend_expiration(struct device *dev);
 extern void pm_runtime_update_max_time_suspended(struct device *dev,
 						 s64 delta_ns);
 extern void pm_runtime_set_memalloc_noio(struct device *dev, bool enable);
@@ -105,7 +105,7 @@ static inline bool pm_runtime_callbacks_present(struct device *dev)
 
 static inline void pm_runtime_mark_last_busy(struct device *dev)
 {
-	WRITE_ONCE(dev->power.last_busy, jiffies);
+	WRITE_ONCE(dev->power.last_busy, ktime_to_ns(ktime_get()));
 }
 
 static inline bool pm_runtime_is_irq_safe(struct device *dev)
@@ -168,7 +168,7 @@ static inline void __pm_runtime_use_autosuspend(struct device *dev,
 						bool use) {}
 static inline void pm_runtime_set_autosuspend_delay(struct device *dev,
 						int delay) {}
-static inline unsigned long pm_runtime_autosuspend_expiration(
+static inline u64 pm_runtime_autosuspend_expiration(
 				struct device *dev) { return 0; }
 static inline void pm_runtime_set_memalloc_noio(struct device *dev,
 						bool enable){}