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 system which sometimes wants
duration in the range of 1 ms.
We can move autosuspend on hrtimer to get finer granularity for short
duration and takes advantage of slack to keep some margins and gathers
long timeout in minimum wakeups.
On an arm64 platform that uses 1ms for autosuspending timeout of its GPU,
the power consumption improves by 10% for idle use case 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 2119884 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@xxxxxxxxxx>
---
drivers/base/power/runtime.c | 63 ++++++++++++++++++++++++--------------------
include/linux/pm.h | 5 ++--
include/linux/pm_runtime.h | 6 ++---
3 files changed, 40 insertions(+), 34 deletions(-)
diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
index beb85c3..7062469 100644
--- a/drivers/base/power/runtime.c
+++ b/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);
}
diff --git a/include/linux/pm.h b/include/linux/pm.h
index e723b78..0bd9de1 100644
--- a/include/linux/pm.h
+++ b/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;
diff --git a/include/linux/pm_runtime.h b/include/linux/pm_runtime.h
index f0fc470..54af4ee 100644
--- a/include/linux/pm_runtime.h
+++ b/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){}
--
2.7.4
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