Re: Async suspend-resume patch w/ completions (was: Re: Async suspend-resume patch w/ rwsems)

From: Rafael J. Wysocki
Date: Thu Dec 10 2009 - 18:45:40 EST

On Thursday 10 December 2009, Alan Stern wrote:
> On Thu, 10 Dec 2009, Rafael J. Wysocki wrote:
>
> > > You should see how badly lockdep complains about the rwsems. If it
> > > really doesn't like them then using completions makes sense.
> >
> > It does complain about them, but when the nested _down operations are marked
> > as nested, it stops complaining (that's in the version where there's no async
> > in the _noirq phases).
>
> Did you set the async_suspend flag for any devices during the test?

Yes. All ACPI, all PCI, all serio, as usual. ;-)

> And did you run more than one suspend/resume cycle?

Sure. Actually, I test it in the /sys/power/pm_test = core mode, but that
shouldn't really matter.

> > +extern int __dpm_wait(struct device *dev, void *ign);
> > +
> > +static inline void dpm_wait(struct device *dev)
> > +{
> > + __dpm_wait(dev, NULL);
> > +}
>
> Sorry, I intended to mention this before but forgot. This design is
> inelegant. You shouldn't have inlines calling functions with extra
> unused arguments; they just waste code space. Make dpm_wait() be a
> real routine and add a shim to the device_for_each_child() loop.

I thought about that myself, done now.

> > @@ -366,7 +388,7 @@ void dpm_resume_noirq(pm_message_t state
> >
> > mutex_lock(&dpm_list_mtx);
> > transition_started = false;
> > - list_for_each_entry(dev, &dpm_list, power.entry)
> > + list_for_each_entry(dev, &dpm_list, power.entry) {
> > if (dev->power.status > DPM_OFF) {
> > int error;
> >
> > @@ -375,23 +397,27 @@ void dpm_resume_noirq(pm_message_t state
> > if (error)
> > pm_dev_err(dev, state, " early", error);
> > }
> > + /* Needed by the subsequent dpm_resume(). */
> > + INIT_COMPLETION(dev->power.completion);
>
> You're still doing it. Don't initialize the completions in a totally
> different phase! Initialize them directly before they are used.
> Namely, at the start of device_resume() and device_suspend().

The idea was to initialize them all at the same time, before entering the
phase in which they were used, but I came to the conclusion that this was not
necessary, because the dpm_list ordering was such that the devices to be waited
for would always have their completions reinitialized before starting
__device_suspend() or __device_resume() for the waiting ones.

> One more thing. A logical time to check for errors is just after
> waiting for the children in __device_suspend(), instead of beforehand
> in async_suspend(). After all, if an error occurs then it's likely to
> happen while we are waiting.

Good idea, done.

Updated patch is appended.

Rafael


---
drivers/base/power/main.c | 106 ++++++++++++++++++++++++++++++++++++++++---
include/linux/device.h | 6 ++
include/linux/pm.h | 7 ++
include/linux/resume-trace.h | 7 ++
4 files changed, 121 insertions(+), 5 deletions(-)

Index: linux-2.6/include/linux/pm.h
===================================================================
--- linux-2.6.orig/include/linux/pm.h
+++ linux-2.6/include/linux/pm.h
@@ -26,6 +26,7 @@
#include <linux/spinlock.h>
#include <linux/wait.h>
#include <linux/timer.h>
+#include <linux/completion.h>

/*
* Callbacks for platform drivers to implement.
@@ -412,9 +413,11 @@ struct dev_pm_info {
pm_message_t power_state;
unsigned int can_wakeup:1;
unsigned int should_wakeup:1;
+ unsigned async_suspend:1;
enum dpm_state status; /* Owned by the PM core */
#ifdef CONFIG_PM_SLEEP
struct list_head entry;
+ struct completion completion;
#endif
#ifdef CONFIG_PM_RUNTIME
struct timer_list suspend_timer;
@@ -508,6 +511,8 @@ extern void __suspend_report_result(cons
__suspend_report_result(__func__, fn, ret); \
} while (0)

+extern void dpm_wait(struct device *dev);
+
#else /* !CONFIG_PM_SLEEP */

#define device_pm_lock() do {} while (0)
@@ -520,6 +525,8 @@ static inline int dpm_suspend_start(pm_m

#define suspend_report_result(fn, ret) do {} while (0)

+static inline void dpm_wait(struct device *dev) {}
+
#endif /* !CONFIG_PM_SLEEP */

/* How to reorder dpm_list after device_move() */
Index: linux-2.6/drivers/base/power/main.c
===================================================================
--- linux-2.6.orig/drivers/base/power/main.c
+++ linux-2.6/drivers/base/power/main.c
@@ -25,6 +25,7 @@
#include <linux/resume-trace.h>
#include <linux/rwsem.h>
#include <linux/interrupt.h>
+#include <linux/async.h>

#include "../base.h"
#include "power.h"
@@ -42,6 +43,7 @@
LIST_HEAD(dpm_list);

static DEFINE_MUTEX(dpm_list_mtx);
+static pm_message_t pm_transition;

/*
* Set once the preparation of devices for a PM transition has started, reset
@@ -56,6 +58,7 @@ static bool transition_started;
void device_pm_init(struct device *dev)
{
dev->power.status = DPM_ON;
+ init_completion(&dev->power.completion);
pm_runtime_init(dev);
}

@@ -111,6 +114,7 @@ void device_pm_remove(struct device *dev
pr_debug("PM: Removing info for %s:%s\n",
dev->bus ? dev->bus->name : "No Bus",
kobject_name(&dev->kobj));
+ complete_all(&dev->power.completion);
mutex_lock(&dpm_list_mtx);
list_del_init(&dev->power.entry);
mutex_unlock(&dpm_list_mtx);
@@ -162,6 +166,28 @@ void device_pm_move_last(struct device *
}

/**
+ * dpm_wait - Wait for a PM operation to complete.
+ * @dev: Device to wait for.
+ */
+void dpm_wait(struct device *dev)
+{
+ if (dev)
+ wait_for_completion(&dev->power.completion);
+}
+EXPORT_SYMBOL_GPL(dpm_wait);
+
+static int dpm_wait_fn(struct device *dev, void *ignore)
+{
+ dpm_wait(dev);
+ return 0;
+}
+
+static void dpm_wait_for_children(struct device *dev)
+{
+ device_for_each_child(dev, NULL, dpm_wait_fn);
+}
+
+/**
* pm_op - Execute the PM operation appropriate for given PM event.
* @dev: Device to handle.
* @ops: PM operations to choose from.
@@ -381,17 +407,18 @@ void dpm_resume_noirq(pm_message_t state
EXPORT_SYMBOL_GPL(dpm_resume_noirq);

/**
- * device_resume - Execute "resume" callbacks for given device.
+ * __device_resume - Execute "resume" callbacks for given device.
* @dev: Device to handle.
* @state: PM transition of the system being carried out.
*/
-static int device_resume(struct device *dev, pm_message_t state)
+static int __device_resume(struct device *dev, pm_message_t state)
{
int error = 0;

TRACE_DEVICE(dev);
TRACE_RESUME(0);

+ dpm_wait(dev->parent);
down(&dev->sem);

if (dev->bus) {
@@ -426,11 +453,34 @@ static int device_resume(struct device *
}
End:
up(&dev->sem);
+ complete_all(&dev->power.completion);

TRACE_RESUME(error);
return error;
}

+static void async_resume(void *data, async_cookie_t cookie)
+{
+ struct device *dev = (struct device *)data;
+ int error;
+
+ error = __device_resume(dev, pm_transition);
+ if (error)
+ pm_dev_err(dev, pm_transition, " async", error);
+ put_device(dev);
+}
+
+static int device_resume(struct device *dev)
+{
+ if (dev->power.async_suspend && !pm_trace_is_enabled()) {
+ get_device(dev);
+ async_schedule(async_resume, dev);
+ return 0;
+ }
+
+ return __device_resume(dev, pm_transition);
+}
+
/**
* dpm_resume - Execute "resume" callbacks for non-sysdev devices.
* @state: PM transition of the system being carried out.
@@ -444,6 +494,7 @@ static void dpm_resume(pm_message_t stat

INIT_LIST_HEAD(&list);
mutex_lock(&dpm_list_mtx);
+ pm_transition = state;
while (!list_empty(&dpm_list)) {
struct device *dev = to_device(dpm_list.next);

@@ -451,10 +502,11 @@ static void dpm_resume(pm_message_t stat
if (dev->power.status >= DPM_OFF) {
int error;

+ INIT_COMPLETION(dev->power.completion);
dev->power.status = DPM_RESUMING;
mutex_unlock(&dpm_list_mtx);

- error = device_resume(dev, state);
+ error = device_resume(dev);

mutex_lock(&dpm_list_mtx);
if (error)
@@ -469,6 +521,7 @@ static void dpm_resume(pm_message_t stat
}
list_splice(&list, &dpm_list);
mutex_unlock(&dpm_list_mtx);
+ async_synchronize_full();
}

/**
@@ -623,17 +676,23 @@ int dpm_suspend_noirq(pm_message_t state
}
EXPORT_SYMBOL_GPL(dpm_suspend_noirq);

+static int async_error;
+
/**
* device_suspend - Execute "suspend" callbacks for given device.
* @dev: Device to handle.
* @state: PM transition of the system being carried out.
*/
-static int device_suspend(struct device *dev, pm_message_t state)
+static int __device_suspend(struct device *dev, pm_message_t state)
{
int error = 0;

+ dpm_wait_for_children(dev);
down(&dev->sem);

+ if (async_error)
+ goto End;
+
if (dev->class) {
if (dev->class->pm) {
pm_dev_dbg(dev, state, "class ");
@@ -666,12 +725,42 @@ static int device_suspend(struct device
suspend_report_result(dev->bus->suspend, error);
}
}
+
+ if (!error)
+ dev->power.status = DPM_OFF;
+
End:
up(&dev->sem);
+ complete_all(&dev->power.completion);

return error;
}

+static void async_suspend(void *data, async_cookie_t cookie)
+{
+ struct device *dev = (struct device *)data;
+ int error;
+
+ error = __device_suspend(dev, pm_transition);
+ if (error) {
+ pm_dev_err(dev, pm_transition, " async", error);
+ async_error = error;
+ }
+
+ put_device(dev);
+}
+
+static int device_suspend(struct device *dev, pm_message_t state)
+{
+ if (dev->power.async_suspend) {
+ get_device(dev);
+ async_schedule(async_suspend, dev);
+ return 0;
+ }
+
+ return __device_suspend(dev, pm_transition);
+}
+
/**
* dpm_suspend - Execute "suspend" callbacks for all non-sysdev devices.
* @state: PM transition of the system being carried out.
@@ -683,10 +772,12 @@ static int dpm_suspend(pm_message_t stat

INIT_LIST_HEAD(&list);
mutex_lock(&dpm_list_mtx);
+ pm_transition = state;
while (!list_empty(&dpm_list)) {
struct device *dev = to_device(dpm_list.prev);

get_device(dev);
+ INIT_COMPLETION(dev->power.completion);
mutex_unlock(&dpm_list_mtx);

error = device_suspend(dev, state);
@@ -697,13 +788,17 @@ static int dpm_suspend(pm_message_t stat
put_device(dev);
break;
}
- dev->power.status = DPM_OFF;
if (!list_empty(&dev->power.entry))
list_move(&dev->power.entry, &list);
put_device(dev);
+ if (async_error)
+ break;
}
list_splice(&list, dpm_list.prev);
mutex_unlock(&dpm_list_mtx);
+ async_synchronize_full();
+ if (!error)
+ error = async_error;
return error;
}

@@ -762,6 +857,7 @@ static int dpm_prepare(pm_message_t stat
INIT_LIST_HEAD(&list);
mutex_lock(&dpm_list_mtx);
transition_started = true;
+ async_error = 0;
while (!list_empty(&dpm_list)) {
struct device *dev = to_device(dpm_list.next);

Index: linux-2.6/include/linux/resume-trace.h
===================================================================
--- linux-2.6.orig/include/linux/resume-trace.h
+++ linux-2.6/include/linux/resume-trace.h
@@ -6,6 +6,11 @@

extern int pm_trace_enabled;

+static inline int pm_trace_is_enabled(void)
+{
+ return pm_trace_enabled;
+}
+
struct device;
extern void set_trace_device(struct device *);
extern void generate_resume_trace(const void *tracedata, unsigned int user);
@@ -17,6 +22,8 @@ extern void generate_resume_trace(const

#else

+static inline int pm_trace_is_enabled(void) { return 0; }
+
#define TRACE_DEVICE(dev) do { } while (0)
#define TRACE_RESUME(dev) do { } while (0)

Index: linux-2.6/include/linux/device.h
===================================================================
--- linux-2.6.orig/include/linux/device.h
+++ linux-2.6/include/linux/device.h
@@ -472,6 +472,12 @@ static inline int device_is_registered(s
return dev->kobj.state_in_sysfs;
}

+static inline void device_enable_async_suspend(struct device *dev, bool enable)
+{
+ if (dev->power.status == DPM_ON)
+ dev->power.async_suspend = enable;
+}
+
void driver_init(void);

/*
--
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