Re: [RFC][PATCH 6/8] PM / Sleep: Implement opportunistic sleep

From: Rafael J. Wysocki
Date: Thu Apr 26 2012 - 17:48:14 EST


On Thursday, April 26, 2012, NeilBrown wrote:
> On Sun, 22 Apr 2012 23:23:23 +0200 "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
>
> > From: "Rafael J. Wysocki" <rjw@xxxxxxx>
> > To: Linux PM list <linux-pm@xxxxxxxxxxxxxxx>
> > Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, Magnus Damm <magnus.damm@xxxxxxxxx>, markgross@xxxxxxxxxxx, Matthew Garrett <mjg@xxxxxxxxxx>, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>, Arve HjÃnnevÃg <arve@xxxxxxxxxxx>, John Stultz <john.stultz@xxxxxxxxxx>, Brian Swetland <swetland@xxxxxxxxxx>, Neil Brown <neilb@xxxxxxx>, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>, Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>, "Srivatsa S. Bhat" <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> > Subject: [RFC][PATCH 6/8] PM / Sleep: Implement opportunistic sleep
> > Date: Sun, 22 Apr 2012 23:23:23 +0200
> > Sender: linux-kernel-owner@xxxxxxxxxxxxxxx
> > User-Agent: KMail/1.13.6 (Linux/3.4.0-rc3+; KDE/4.6.0; x86_64; ; )
> >
> > From: Rafael J. Wysocki <rjw@xxxxxxx>
> >
> > Introduce a mechanism by which the kernel can trigger global
> > transitions to a sleep state chosen by user space if there are no
> > active wakeup sources.
>
> Hi Rafael,

Hi,

> just a few little issues below. Over all I think that if we have to have
> auto-sleep in the kernel, then this is a good way to do it.

Good, we seem to agree in principle, then. :-)

> > +static void try_to_suspend(struct work_struct *work)
> > +{
> > + unsigned int initial_count, final_count;
> > +
> > + if (!pm_get_wakeup_count(&initial_count, true))
> > + goto out;
> > +
> > + mutex_lock(&autosleep_lock);
> > +
> > + if (!pm_save_wakeup_count(initial_count)) {
> > + mutex_unlock(&autosleep_lock);
> > + goto out;
> > + }
> > +
> > + if (autosleep_state == PM_SUSPEND_ON) {
> > + mutex_unlock(&autosleep_lock);
> > + return;
> > + }
> > + if (autosleep_state >= PM_SUSPEND_MAX)
> > + hibernate();
> > + else
> > + pm_suspend(autosleep_state);
> > +
> > + mutex_unlock(&autosleep_lock);
> > +
> > + if (!pm_get_wakeup_count(&final_count, false))
> > + goto out;
> > +
> > + if (final_count == initial_count)
> > + schedule_timeout(HZ / 2);
>
> This doesn't do what you seem to expect it to do.
> You need to set current->state to something like TASK_UNINTERRUPTIBLE
> before calling schedule_timeout, otherwise it is effectily a no-op.
> schedule_timeout_uninterruptible(), for example, will do this for you.

Right. I obviously overlooked the missing state change.

> However the value of this isn't clear to me, so a comment would probably be a
> good thing.
> This continue presumably fires if we wake up without any wakeup sources
> being activated. In that case you want to delay for 500ms - presumably to
> avoid a tight suspend/resume loop if something goes wrong?

Yes.

> I have occasionally seen a stray/uninteresting interrupt wake from suspend
> immediately after entering suspend and the next attempt succeeds. Maybe this
> is a bug in some driver somewhere, but not a big one. I think I would rather
> in that case that we attempt to re-enter suspend immediately. Maybe after a
> few failed attempts it makes sense to back off.

Perhaps. We can adjust this particular thing later, I think.

> The other question is: if we want to back-off, is 500ms really enough? What
> will be gained by, or could be achieved in, that time? An exponential
> back-off might be defensible, but I can't see the value of a 500ms fixed
> back-off.
> However if you can, I'd love to see a comment in there explaining it.

Sure.

> > +
> > + out:
> > + queue_up_suspend_work();
> > +}
> > +
>
>
> > +
> > +int pm_autosleep_set_state(suspend_state_t state)
> > +{
> > +
> > +#ifndef CONFIG_HIBERNATION
> > + if (state >= PM_SUSPEND_MAX)
> > + return -EINVAL;
> > +#endif
> > +
> > + __pm_stay_awake(autosleep_ws);
> > +
> > + mutex_lock(&autosleep_lock);
> > +
> > + autosleep_state = state;
> > +
> > + __pm_relax(autosleep_ws);
>
> I'm struggling to see the point of the autosleep_ws.
>
> A suspend cannot actually happen while this code is running (can it?) because
> it will wait for the process to enter the freezer.
> So the only effect of this is:
> 1/ cause the current auto-sleep cycle to abort and
> 2/ maybe add some accounting number is the autosleep_ws.
> Is that right?
> Which of these is needed?

This is to solve a problem when user space attempts to echo "off" to
/sys/power/autosleep exactly when pm_suspend() is initiated as a part
of autosleep under the autosleep lock. In that case, if autosleep_ws is not
there, the process wanting to disable autosleep will have to wait for the
pm_suspend() to complete (unless it holds a wakelock), which is suboptimal.

> I would imagine that any process writing to /sys/power/autosleep would be
> holding a wakelock, and if it didn't it should expect things to be racy...
>
> Am I missing something?

The assumption above is kind of optimistic in my opinion. That process
very well may be a system administrator's bash, for example. :-)

> > +
> > + if (state > PM_SUSPEND_ON)
> > + queue_up_suspend_work();
>
> The test here is superfluous as queue_up_suspend_work() itself tests that
> 'state' is > PM_SUSPEND_ON. However maybe it is more readable this way, so I
> won't object it you like it.

Well, patch [7/8] adds the second statement under this conditional,
so I'd prefer to keep it the current way.

> > +
> > + mutex_unlock(&autosleep_lock);
> > + return 0;
> > +}
>
>
> > @@ -339,7 +359,8 @@ static ssize_t wakeup_count_show(struct
> > {
> > unsigned int val;
> >
> > - return pm_get_wakeup_count(&val) ? sprintf(buf, "%u\n", val) : -EINTR;
> > + return pm_get_wakeup_count(&val, true) ?
> > + sprintf(buf, "%u\n", val) : -EINTR;
> > }
>
> I think it would be really nice for user-space auto-suspend if the 'block'
> flag to be settable from the O_NONBLOCK setting. And for poll() to work
> on /sys/power/wakeup-count. However this would require a bit of surgery on
> sysfs. So that is a "maybe later", but having the 'block' flag in there is
> a step in the right direction.

Yes, "maybe later" is what I think about that too. :-)

> >
> > static ssize_t wakeup_count_store(struct kobject *kobj,
> > @@ -347,15 +368,69 @@ static ssize_t wakeup_count_store(struct
> > const char *buf, size_t n)
> > {
> > unsigned int val;
> > + int error;
> > +
> > + error = pm_autosleep_lock();
> > + if (error)
> > + return error;
> > +
> > + if (pm_autosleep_state() > PM_SUSPEND_ON) {
> > + error = -EBUSY;
> > + goto out;
> > + }
> >
> > if (sscanf(buf, "%u", &val) == 1) {
> > if (pm_save_wakeup_count(val))
> > return n;
>
> You need a 'pm_autosleep_unlock() in there - or possibly
> error = n; goto out;

Right, thanks for spotting this!

> > }
> > - return -EINVAL;
> > + error = -EINVAL;
> > +
> > + out:
> > + pm_autosleep_unlock();
> > + return error;
> > }
>
> > core_initcall(pm_init);
> > Index: linux/drivers/base/power/wakeup.c
> > ===================================================================
> > --- linux.orig/drivers/base/power/wakeup.c
> > +++ linux/drivers/base/power/wakeup.c
> > @@ -498,8 +498,10 @@ static void wakeup_source_deactivate(str
> > trace_wakeup_source_deactivate(ws->name, cec);
> >
> > split_counters(&cnt, &inpr);
> > - if (!inpr && waitqueue_active(&wakeup_count_wait_queue))
> > + if (!inpr && waitqueue_active(&wakeup_count_wait_queue)) {
> > wake_up(&wakeup_count_wait_queue);
> > + queue_up_suspend_work();
> > + }
>
> This doesn't look right. suspend_work always requeues itself unless
> autosleep_state == PM_SUSPEND_ON, and whenver autosleep_state is set we
> already call queue_up_suspend_work(). So there is no need to call it here.

OK, I agree. Good, I don't have to add more code to wakeup_source_deactivate(). :-)

> > Index: linux/Documentation/ABI/testing/sysfs-power
> > ===================================================================
> > --- linux.orig/Documentation/ABI/testing/sysfs-power
> > +++ linux/Documentation/ABI/testing/sysfs-power
> > @@ -172,3 +172,20 @@ Description:
> >
> > Reading from this file will display the current value, which is
> > set to 1 MB by default.
> > +
> > +What: /sys/power/autosleep
> > +Date: February 2012
> > +Contact: Rafael J. Wysocki <rjw@xxxxxxx>
> > +Description:
> > + The /sys/power/autosleep file can be written one of the strings
>
> "To the .. file can be written..." or
> "The .. file can have written ..." or
> "One of the strings returned by (reads from) /sys/power/state can be written
> to the file ..."
> ??
> > + returned by reads from /sys/power/state. If that happens, a
> > + work item attempting to trigger a transition of the system to
> > + the sleep state represented by that string is queued up. This
> > + attempt will only succeed if there are no active wakeup sources
> > + in the system at that time. After evey execution, regardless
> ^^^^
> "every"
>
> > + of whether or not the attempt to put the system to sleep has
> > + succeeded, the work item requeues itself until user space
> > + writes "off" to /sys/power/autosleep.
> > +
> > + Reading from this file causes the last string successfully
> > + written to it to be displayed.
> ^^^^^^^^^ "returned".

Well spotted, thanks!

Below is an updated patch hopefully addressing your comments.

Thanks,
Rafael

---
From: Rafael J. Wysocki <rjw@xxxxxxx>
Subject: PM / Sleep: Implement opportunistic sleep, v2

Introduce a mechanism by which the kernel can trigger global
transitions to a sleep state chosen by user space if there are no
active wakeup sources.

It consists of a new sysfs attribute, /sys/power/autosleep, that
can be written one of the strings returned by reads from
/sys/power/state, an ordered workqueue and a work item carrying out
the "suspend" operations. If a string representing the system's
sleep state is written to /sys/power/autosleep, the work item
triggering transitions to that state is queued up and it requeues
itself after every execution until user space writes "off" to
/sys/power/autosleep.

That work item enables the detection of wakeup events using the
functions already defined in drivers/base/power/wakeup.c (with one
small modification) and calls either pm_suspend(), or hibernate() to
put the system into a sleep state. If a wakeup event is reported
while the transition is in progress, it will abort the transition and
the "system suspend" work item will be queued up again.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-power | 17 ++++
drivers/base/power/wakeup.c | 34 +++++----
include/linux/suspend.h | 13 +++
kernel/power/Kconfig | 8 ++
kernel/power/Makefile | 1
kernel/power/autosleep.c | 117 +++++++++++++++++++++++++++++++++
kernel/power/main.c | 119 ++++++++++++++++++++++++++++------
kernel/power/power.h | 18 +++++
8 files changed, 292 insertions(+), 35 deletions(-)

Index: linux/kernel/power/Makefile
===================================================================
--- linux.orig/kernel/power/Makefile
+++ linux/kernel/power/Makefile
@@ -9,5 +9,6 @@ obj-$(CONFIG_SUSPEND) += suspend.o
obj-$(CONFIG_PM_TEST_SUSPEND) += suspend_test.o
obj-$(CONFIG_HIBERNATION) += hibernate.o snapshot.o swap.o user.o \
block_io.o
+obj-$(CONFIG_PM_AUTOSLEEP) += autosleep.o

obj-$(CONFIG_MAGIC_SYSRQ) += poweroff.o
Index: linux/kernel/power/Kconfig
===================================================================
--- linux.orig/kernel/power/Kconfig
+++ linux/kernel/power/Kconfig
@@ -103,6 +103,14 @@ config PM_SLEEP_SMP
select HOTPLUG
select HOTPLUG_CPU

+config PM_AUTOSLEEP
+ bool "Opportunistic sleep"
+ depends on PM_SLEEP
+ default n
+ ---help---
+ Allow the kernel to trigger a system transition into a global sleep
+ state automatically whenever there are no active wakeup sources.
+
config PM_RUNTIME
bool "Run-time PM core functionality"
depends on !IA64_HP_SIM
Index: linux/kernel/power/power.h
===================================================================
--- linux.orig/kernel/power/power.h
+++ linux/kernel/power/power.h
@@ -264,3 +264,21 @@ static inline void suspend_thaw_processe
{
}
#endif
+
+#ifdef CONFIG_PM_AUTOSLEEP
+
+/* kernel/power/autosleep.c */
+extern int pm_autosleep_init(void);
+extern int pm_autosleep_lock(void);
+extern void pm_autosleep_unlock(void);
+extern suspend_state_t pm_autosleep_state(void);
+extern int pm_autosleep_set_state(suspend_state_t state);
+
+#else /* !CONFIG_PM_AUTOSLEEP */
+
+static inline int pm_autosleep_init(void) { return 0; }
+static inline int pm_autosleep_lock(void) { return 0; }
+static inline void pm_autosleep_unlock(void) {}
+static inline suspend_state_t pm_autosleep_state(void) { return PM_SUSPEND_ON; }
+
+#endif /* !CONFIG_PM_AUTOSLEEP */
Index: linux/include/linux/suspend.h
===================================================================
--- linux.orig/include/linux/suspend.h
+++ linux/include/linux/suspend.h
@@ -356,7 +356,7 @@ extern int unregister_pm_notifier(struct
extern bool events_check_enabled;

extern bool pm_wakeup_pending(void);
-extern bool pm_get_wakeup_count(unsigned int *count);
+extern bool pm_get_wakeup_count(unsigned int *count, bool block);
extern bool pm_save_wakeup_count(unsigned int count);

static inline void lock_system_sleep(void)
@@ -407,6 +407,17 @@ static inline void unlock_system_sleep(v

#endif /* !CONFIG_PM_SLEEP */

+#ifdef CONFIG_PM_AUTOSLEEP
+
+/* kernel/power/autosleep.c */
+void queue_up_suspend_work(void);
+
+#else /* !CONFIG_PM_AUTOSLEEP */
+
+static inline void queue_up_suspend_work(void) {}
+
+#endif /* !CONFIG_PM_AUTOSLEEP */
+
#ifdef CONFIG_ARCH_SAVE_PAGE_KEYS
/*
* The ARCH_SAVE_PAGE_KEYS functions can be used by an architecture
Index: linux/kernel/power/autosleep.c
===================================================================
--- /dev/null
+++ linux/kernel/power/autosleep.c
@@ -0,0 +1,117 @@
+/*
+ * kernel/power/autosleep.c
+ *
+ * Opportunistic sleep support.
+ *
+ * Copyright (C) 2012 Rafael J. Wysocki <rjw@xxxxxxx>
+ */
+
+#include <linux/device.h>
+#include <linux/mutex.h>
+#include <linux/pm_wakeup.h>
+
+#include "power.h"
+
+static suspend_state_t autosleep_state;
+static struct workqueue_struct *autosleep_wq;
+static DEFINE_MUTEX(autosleep_lock);
+static struct wakeup_source *autosleep_ws;
+
+static void try_to_suspend(struct work_struct *work)
+{
+ unsigned int initial_count, final_count;
+
+ if (!pm_get_wakeup_count(&initial_count, true))
+ goto out;
+
+ mutex_lock(&autosleep_lock);
+
+ if (!pm_save_wakeup_count(initial_count)) {
+ mutex_unlock(&autosleep_lock);
+ goto out;
+ }
+
+ if (autosleep_state == PM_SUSPEND_ON) {
+ mutex_unlock(&autosleep_lock);
+ return;
+ }
+ if (autosleep_state >= PM_SUSPEND_MAX)
+ hibernate();
+ else
+ pm_suspend(autosleep_state);
+
+ mutex_unlock(&autosleep_lock);
+
+ if (!pm_get_wakeup_count(&final_count, false))
+ goto out;
+
+ /*
+ * If the wakeup occured for an unknown reason, wait to prevent the
+ * system from trying to suspend and waking up in a tight loop.
+ */
+ if (final_count == initial_count)
+ schedule_timeout_uninterruptible(HZ / 2);
+
+ out:
+ queue_up_suspend_work();
+}
+
+static DECLARE_WORK(suspend_work, try_to_suspend);
+
+void queue_up_suspend_work(void)
+{
+ if (!work_pending(&suspend_work) && autosleep_state > PM_SUSPEND_ON)
+ queue_work(autosleep_wq, &suspend_work);
+}
+
+suspend_state_t pm_autosleep_state(void)
+{
+ return autosleep_state;
+}
+
+int pm_autosleep_lock(void)
+{
+ return mutex_lock_interruptible(&autosleep_lock);
+}
+
+void pm_autosleep_unlock(void)
+{
+ mutex_unlock(&autosleep_lock);
+}
+
+int pm_autosleep_set_state(suspend_state_t state)
+{
+
+#ifndef CONFIG_HIBERNATION
+ if (state >= PM_SUSPEND_MAX)
+ return -EINVAL;
+#endif
+
+ __pm_stay_awake(autosleep_ws);
+
+ mutex_lock(&autosleep_lock);
+
+ autosleep_state = state;
+
+ __pm_relax(autosleep_ws);
+
+ if (state > PM_SUSPEND_ON)
+ queue_up_suspend_work();
+
+ mutex_unlock(&autosleep_lock);
+ return 0;
+}
+
+int __init pm_autosleep_init(void)
+{
+ autosleep_ws = wakeup_source_register("autosleep");
+ if (!autosleep_ws)
+ return -ENOMEM;
+
+ autosleep_wq = alloc_ordered_workqueue("autosleep", 0);
+ if (autosleep_wq)
+ return 0;
+
+ wakeup_source_unregister(autosleep_ws);
+ return -ENOMEM;
+}
Index: linux/kernel/power/main.c
===================================================================
--- linux.orig/kernel/power/main.c
+++ linux/kernel/power/main.c
@@ -269,8 +269,7 @@ static ssize_t state_show(struct kobject
return (s - buf);
}

-static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
- const char *buf, size_t n)
+static suspend_state_t decode_state(const char *buf, size_t n)
{
#ifdef CONFIG_SUSPEND
suspend_state_t state = PM_SUSPEND_STANDBY;
@@ -278,27 +277,48 @@ static ssize_t state_store(struct kobjec
#endif
char *p;
int len;
- int error = -EINVAL;

p = memchr(buf, '\n', n);
len = p ? p - buf : n;

- /* First, check if we are requested to hibernate */
- if (len == 4 && !strncmp(buf, "disk", len)) {
- error = hibernate();
- goto Exit;
- }
+ /* Check hibernation first. */
+ if (len == 4 && !strncmp(buf, "disk", len))
+ return PM_SUSPEND_MAX;

#ifdef CONFIG_SUSPEND
- for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++) {
- if (*s && len == strlen(*s) && !strncmp(buf, *s, len)) {
- error = pm_suspend(state);
- break;
- }
- }
+ for (s = &pm_states[state]; state < PM_SUSPEND_MAX; s++, state++)
+ if (*s && len == strlen(*s) && !strncmp(buf, *s, len))
+ return state;
#endif

- Exit:
+ return PM_SUSPEND_ON;
+}
+
+static ssize_t state_store(struct kobject *kobj, struct kobj_attribute *attr,
+ const char *buf, size_t n)
+{
+ suspend_state_t state;
+ int error;
+
+ error = pm_autosleep_lock();
+ if (error)
+ return error;
+
+ if (pm_autosleep_state() > PM_SUSPEND_ON) {
+ error = -EBUSY;
+ goto out;
+ }
+
+ state = decode_state(buf, n);
+ if (state < PM_SUSPEND_MAX)
+ error = pm_suspend(state);
+ else if (state == PM_SUSPEND_MAX)
+ error = hibernate();
+ else
+ error = -EINVAL;
+
+ out:
+ pm_autosleep_unlock();
return error ? error : n;
}

@@ -339,7 +359,8 @@ static ssize_t wakeup_count_show(struct
{
unsigned int val;

- return pm_get_wakeup_count(&val) ? sprintf(buf, "%u\n", val) : -EINTR;
+ return pm_get_wakeup_count(&val, true) ?
+ sprintf(buf, "%u\n", val) : -EINTR;
}

static ssize_t wakeup_count_store(struct kobject *kobj,
@@ -347,15 +368,69 @@ static ssize_t wakeup_count_store(struct
const char *buf, size_t n)
{
unsigned int val;
+ int error;
+
+ error = pm_autosleep_lock();
+ if (error)
+ return error;
+
+ if (pm_autosleep_state() > PM_SUSPEND_ON) {
+ error = -EBUSY;
+ goto out;
+ }

+ error = -EINVAL;
if (sscanf(buf, "%u", &val) == 1) {
if (pm_save_wakeup_count(val))
- return n;
+ error = n;
}
- return -EINVAL;
+
+ out:
+ pm_autosleep_unlock();
+ return error;
}

power_attr(wakeup_count);
+
+#ifdef CONFIG_PM_AUTOSLEEP
+static ssize_t autosleep_show(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ char *buf)
+{
+ suspend_state_t state = pm_autosleep_state();
+
+ if (state == PM_SUSPEND_ON)
+ return sprintf(buf, "off\n");
+
+#ifdef CONFIG_SUSPEND
+ if (state < PM_SUSPEND_MAX)
+ return sprintf(buf, "%s\n", valid_state(state) ?
+ pm_states[state] : "error");
+#endif
+#ifdef CONFIG_HIBERNATION
+ return sprintf(buf, "disk\n");
+#else
+ return sprintf(buf, "error");
+#endif
+}
+
+static ssize_t autosleep_store(struct kobject *kobj,
+ struct kobj_attribute *attr,
+ const char *buf, size_t n)
+{
+ suspend_state_t state = decode_state(buf, n);
+ int error;
+
+ if (state == PM_SUSPEND_ON
+ && !(strncmp(buf, "off", 3) && strncmp(buf, "off\n", 4)))
+ return -EINVAL;
+
+ error = pm_autosleep_set_state(state);
+ return error ? error : n;
+}
+
+power_attr(autosleep);
+#endif /* CONFIG_PM_AUTOSLEEP */
#endif /* CONFIG_PM_SLEEP */

#ifdef CONFIG_PM_TRACE
@@ -409,6 +484,9 @@ static struct attribute * g[] = {
#ifdef CONFIG_PM_SLEEP
&pm_async_attr.attr,
&wakeup_count_attr.attr,
+#ifdef CONFIG_PM_AUTOSLEEP
+ &autosleep_attr.attr,
+#endif
#ifdef CONFIG_PM_DEBUG
&pm_test_attr.attr,
#endif
@@ -444,7 +522,10 @@ static int __init pm_init(void)
power_kobj = kobject_create_and_add("power", NULL);
if (!power_kobj)
return -ENOMEM;
- return sysfs_create_group(power_kobj, &attr_group);
+ error = sysfs_create_group(power_kobj, &attr_group);
+ if (error)
+ return error;
+ return pm_autosleep_init();
}

core_initcall(pm_init);
Index: linux/drivers/base/power/wakeup.c
===================================================================
--- linux.orig/drivers/base/power/wakeup.c
+++ linux/drivers/base/power/wakeup.c
@@ -660,29 +660,33 @@ bool pm_wakeup_pending(void)
/**
* pm_get_wakeup_count - Read the number of registered wakeup events.
* @count: Address to store the value at.
+ * @block: Whether or not to block.
*
- * Store the number of registered wakeup events at the address in @count. Block
- * if the current number of wakeup events being processed is nonzero.
+ * Store the number of registered wakeup events at the address in @count. If
+ * @block is set, block until the current number of wakeup events being
+ * processed is zero.
*
- * Return 'false' if the wait for the number of wakeup events being processed to
- * drop down to zero has been interrupted by a signal (and the current number
- * of wakeup events being processed is still nonzero). Otherwise return 'true'.
+ * Return 'false' if the current number of wakeup events being processed is
+ * nonzero. Otherwise return 'true'.
*/
-bool pm_get_wakeup_count(unsigned int *count)
+bool pm_get_wakeup_count(unsigned int *count, bool block)
{
unsigned int cnt, inpr;
- DEFINE_WAIT(wait);

- for (;;) {
- prepare_to_wait(&wakeup_count_wait_queue, &wait,
- TASK_INTERRUPTIBLE);
- split_counters(&cnt, &inpr);
- if (inpr == 0 || signal_pending(current))
- break;
+ if (block) {
+ DEFINE_WAIT(wait);

- schedule();
+ for (;;) {
+ prepare_to_wait(&wakeup_count_wait_queue, &wait,
+ TASK_INTERRUPTIBLE);
+ split_counters(&cnt, &inpr);
+ if (inpr == 0 || signal_pending(current))
+ break;
+
+ schedule();
+ }
+ finish_wait(&wakeup_count_wait_queue, &wait);
}
- finish_wait(&wakeup_count_wait_queue, &wait);

split_counters(&cnt, &inpr);
*count = cnt;
Index: linux/Documentation/ABI/testing/sysfs-power
===================================================================
--- linux.orig/Documentation/ABI/testing/sysfs-power
+++ linux/Documentation/ABI/testing/sysfs-power
@@ -172,3 +172,20 @@ Description:

Reading from this file will display the current value, which is
set to 1 MB by default.
+
+What: /sys/power/autosleep
+Date: April 2012
+Contact: Rafael J. Wysocki <rjw@xxxxxxx>
+Description:
+ The /sys/power/autosleep file can be written one of the strings
+ returned by reads from /sys/power/state. If that happens, a
+ work item attempting to trigger a transition of the system to
+ the sleep state represented by that string is queued up. This
+ attempt will only succeed if there are no active wakeup sources
+ in the system at that time. After every execution, regardless
+ of whether or not the attempt to put the system to sleep has
+ succeeded, the work item requeues itself until user space
+ writes "off" to /sys/power/autosleep.
+
+ Reading from this file causes the last string successfully
+ written to it to be returned.
--
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