linux-kernel - Re: [RFC][PATCH] PM / Wakeup: Introduce wakeup source objects and event statistics (was: Re: Wakeup-events implementation)

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Date:	Thu, 9 Sep 2010 01:58:21 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] PM / Wakeup: Introduce wakeup source objects and event statistics (was: Re: Wakeup-events implementation)

On Wednesday, September 08, 2010, Alan Stern wrote:
> On Wed, 8 Sep 2010, Rafael J. Wysocki wrote:
> 
> > Hi,
> > 
> > Below is a patch that adds some statistics to the previously merged
> > pm_wakeup_event()/pm_stay_awake()/pm_relax() code.  It also makes it possible
> > to use wakeup sources that are not directly associated with devices.
> 
> I noted only a few things during a quick read-through.

Great. :-)

> See below.
> 
> > It adds functions for manipulating wakeup source objects and reworks the
> > device wakeup enabling/disabling to use the new functions.  The list of wakeup
> > sources is only used for updating the "hit count" statistics for now (this is
> > the number of times the wakeup source was active when the PM core checked), but
> > I'm planning to add a /proc file listing all wakeup sources, including the ones
> > that are not attached to device objects.
> 
> It must be obvious that this is starting to look more and more like the
> suspend_blockers patch.  What that means or will lead to, I don't
> know...

This actually is intentional, because I want to make it easier for the Android
people to move their stuff towards the mainline, if they want to.

> > It appears to work with the PCI wakeup code added previously, but that's only
> > one case.  I'm also not sure if it builds withoug CONFIG_PM_SLEEP.  [BTW, I'm
> > not sure it atomic_inc() and atomic_dec() imply a memory barrier in general.
> > That seems to be the case on x86, but I don't know about other architectures.]
> 
> They do not imply memory barriers.  See the section on atomic 
> operations in Documentation/memory-barriers.txt.

Ah.  Thanks for the pointer.

> > +/**
> > + * wakeup_source_create - Create a struct wakeup_source object.
> > + * @name: Name of the new wakeup source.
> > + */
> > +struct wakeup_source *wakeup_source_create(const char *name)
> > +{
> > +	struct wakeup_source *ws;
> > +
> > +	ws = kzalloc(sizeof(*ws), GFP_KERNEL);
> > +	if (!ws)
> > +		return NULL;
> > +
> > +	if (name) {
> > +		int len = strlen(name);
> > +		char *s = kzalloc(len + 1, GFP_KERNEL);
> > +		if (s) {
> > +			strncpy(s, name, len);
> 
> Would it be better to use kmalloc instead of kzalloc, call memcpy 
> instead of strncpy, and write the terminating NUL character manually?

Yeah, thanks.

> > +			ws->name = s;
> > +		}
> > +	}
> > +
> > +	return ws;
> > +}
> > +EXPORT_SYMBOL_GPL(wakeup_source_create);
> > +
> > +/**
> > + * wakeup_source_destroy - Destroy a struct wakeup_source object.
> > + * @ws: Wakeup source to destroy.
> > + */
> > +void wakeup_source_destroy(struct wakeup_source *ws)
> > +{
> > +	if (!ws)
> > +		return;
> > +
> > +	spin_lock_irq(&ws->lock);
> 
> Since you use the spinlock here, it needs to be initialized in 
> wakeup_source_create rather than wakeup_source_register.

Yes, thanks.

> > +	while (ws->active) {
> > +		spin_unlock_irq(&ws->lock);
> > +
> > +		schedule_timeout_interruptible(msecs_to_jiffies(TIMEOUT));
> > +
> > +		spin_lock_irq(&ws->lock);
> > +	}
> > +	spin_unlock_irq(&ws->lock);
> > +
> > +	if (ws->name)
> > +		kfree(ws->name);
> 
> No need for the "if".

OK

> > +	kfree(ws);
> > +}
> > +EXPORT_SYMBOL_GPL(wakeup_source_destroy);
> > +
> > +/**
> > + * wakeup_source_register - Add given object to the list of wakeup sources.
> > + * @ws: Wakeup source object to register.
> > + */
> > +void wakeup_source_register(struct wakeup_source *ws)
> > +{
> > +	if (WARN_ON(!ws))
> > +		return;
> > +
> > +	spin_lock_init(&ws->lock);
> > +	setup_timer(&ws->timer, pm_wakeup_timer_fn, (unsigned long)ws);
> > +	ws->active = false;
> > +
> > +	spin_lock_irq(&events_lock);
> > +	list_add_rcu(&ws->entry, &wakeup_sources);
> > +	spin_unlock_irq(&events_lock);
> > +	synchronize_rcu();
> > +}
> > +EXPORT_SYMBOL_GPL(wakeup_source_register);
> 
> ...
> 
> > +/**
> > + * wakeup_source_add - Create and register a wakeup source object.
> > + * @name: Name of the wakeup source to create.
> > + */
> > +struct wakeup_source *wakeup_source_add(const char *name)
> > +{
> > +	struct wakeup_source *ws;
> > +
> > +	ws = wakeup_source_create(name);
> > +	if (ws)
> > +		wakeup_source_register(ws);
> > +
> > +	return ws;
> > +}
> > +EXPORT_SYMBOL_GPL(wakeup_source_add);
> 
> Your use of names is backward.  Normally the *_register routine does
> *_init followed by *_add.

Hmm, I haven't noticed that.  Thanks for the heads up. :-)

> I haven't looked through the rest in enough detail yet to make any 
> meaningful comments.

Sure.  Thanks a lot for your comments so far!

Rafael
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