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Message-Id: <201007012208.11464.rjw@sisk.pl>
Date: Thu, 1 Jul 2010 22:08:11 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Alan Stern <stern@...land.harvard.edu>
Cc: linux-pm@...ts.linux-foundation.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Neil Brown <neilb@...e.de>,
Matthew Garrett <mjg59@...f.ucam.org>,
mark gross <640e9920@...il.com>,
Arve Hjønnevåg <arve@...roid.com>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
Florian Mickler <florian@...kler.org>,
linux-pci@...r.kernel.org, Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [update] Re: [PATCH] PM: Make it possible to avoid wakeup events from being lost
On Thursday, July 01, 2010, Alan Stern wrote:
> On Thu, 1 Jul 2010, Rafael J. Wysocki wrote:
>
> > I invented a slightly different version in the meantime, which is appended
> > as a patch on top of the original one (I don't want to modify the original
> > patch, since it's been reviewed already by several people and went to my
> > linux-next branch).
>
> > /**
> > - * pm_wakeup_work_fn - Deferred closing of a wakeup event.
> > + * pm_wakeup_timer_fn - Deferred closing of a wakeup event.
> > *
> > * Execute pm_relax() for a wakeup event detected in the past and free the
> > * work item object used for queuing up the work.
> > */
> > -static void pm_wakeup_work_fn(struct work_struct *work)
> > +static void pm_wakeup_timer_fn(unsigned long data)
> > {
> > - struct delayed_work *dwork = to_delayed_work(work);
> > + unsigned long flags;
> >
> > - pm_relax();
> > - kfree(dwork);
> > + spin_lock_irqsave(&events_lock, flags);
> > + if (events_timer_expires && time_after(jiffies, events_timer_expires)) {
>
> Should be time_after_eq.
Yes, it should.
> > + events_in_progress -= delayed_count;
> > + event_count += delayed_count;
> > + delayed_count = 0;
> > + events_timer_expires = 0;
> > + }
> > + spin_unlock_irqrestore(&events_lock, flags);
> > }
> >
> > /**
> > @@ -132,19 +145,31 @@ static void pm_wakeup_work_fn(struct wor
> > void pm_wakeup_event(struct device *dev, unsigned int msec)
> > {
> > unsigned long flags;
> > - struct delayed_work *dwork;
> > -
> > - dwork = msec ? kzalloc(sizeof(*dwork), GFP_ATOMIC) : NULL;
> >
> > spin_lock_irqsave(&events_lock, flags);
> > if (dev)
> > dev->power.wakeup_count++;
> >
> > - if (dwork) {
> > - INIT_DELAYED_WORK(dwork, pm_wakeup_work_fn);
> > - schedule_delayed_work(dwork, msecs_to_jiffies(msec));
> > + if (msec) {
> > + ktime_t kt;
> > + struct timespec ts;
> > + unsigned long expires;
> > +
> > + kt = ktime_get();
> > + kt = ktime_add_ns(kt, msec * NSEC_PER_MSEC);
> > + ts = ktime_to_timespec(kt);
> > + expires = timespec_to_jiffies(&ts);
>
> Is this somehow better than jiffies + msecs_to_jiffies(msec)?
I'm not sure about overflows. That said, the "+" version is used in many
places, so there's no problem I think.
> > + if (!expires)
> > + expires = 1;
> > +
> > + if (!events_timer_expires
> > + || time_after(expires, events_timer_expires)) {
> > + mod_timer(&events_timer, expires);
> > + events_timer_expires = expires;
> > + }
> >
> > events_in_progress++;
> > + delayed_count++;
> > } else {
> > event_count++;
> > }
I think your version is better for a few reasons, so I created the appended
patch.
Rafael
---
Subject: PM: Do not use dynamically allocated objects in pm_wakeup_event()
Originally, pm_wakeup_event() uses struct delayed_work objects,
allocated with GFP_ATOMIC, to schedule the execution of pm_relax()
in future. However, as noted by Alan Stern, it is not necessary to
do that, because all pm_wakeup_event() calls can use one static timer
that will always be set to expire at the latest time passed to
pm_wakeup_event().
The modifications are based on the example code posted by Alan.
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
drivers/base/power/wakeup.c | 57 +++++++++++++++++++++++++++++---------------
1 file changed, 38 insertions(+), 19 deletions(-)
Index: linux-2.6/drivers/base/power/wakeup.c
===================================================================
--- linux-2.6.orig/drivers/base/power/wakeup.c
+++ linux-2.6/drivers/base/power/wakeup.c
@@ -9,6 +9,7 @@
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/sched.h>
+#include <linux/ktime.h>
#include <linux/capability.h>
#include <linux/suspend.h>
#include <linux/pm.h>
@@ -28,6 +29,11 @@ static unsigned long events_in_progress;
static DEFINE_SPINLOCK(events_lock);
+static void pm_wakeup_timer_fn(unsigned long data);
+
+static DEFINE_TIMER(events_timer, pm_wakeup_timer_fn, 0, 0);
+static unsigned long events_timer_expires;
+
/*
* The functions below use the observation that each wakeup event starts a
* period in which the system should not be suspended. The moment this period
@@ -103,17 +109,22 @@ void pm_relax(void)
}
/**
- * pm_wakeup_work_fn - Deferred closing of a wakeup event.
+ * pm_wakeup_timer_fn - Delayed finalization of a wakeup event.
*
- * Execute pm_relax() for a wakeup event detected in the past and free the
- * work item object used for queuing up the work.
+ * Decrease the counter of wakeup events being processed after it was increased
+ * by pm_wakeup_event().
*/
-static void pm_wakeup_work_fn(struct work_struct *work)
+static void pm_wakeup_timer_fn(unsigned long data)
{
- struct delayed_work *dwork = to_delayed_work(work);
+ unsigned long flags;
- pm_relax();
- kfree(dwork);
+ spin_lock_irqsave(&events_lock, flags);
+ if (events_timer_expires
+ && time_before_eq(events_timer_expires, jiffies)) {
+ events_in_progress--;
+ events_timer_expires = 0;
+ }
+ spin_unlock_irqrestore(&events_lock, flags);
}
/**
@@ -123,30 +134,38 @@ static void pm_wakeup_work_fn(struct wor
*
* Notify the PM core of a wakeup event (signaled by @dev) that will take
* approximately @msec milliseconds to be processed by the kernel. Increment
- * the counter of wakeup events being processed and queue up a work item
- * that will execute pm_relax() for the event after @msec milliseconds. If @dev
- * is not NULL, the counter of wakeup events related to @dev is incremented too.
+ * the counter of registered wakeup events and (if @msec is nonzero) set up
+ * the wakeup events timer to execute pm_wakeup_timer_fn() in future (if the
+ * timer has not been set up already, increment the counter of wakeup events
+ * being processed). If @dev is not NULL, the counter of wakeup events related
+ * to @dev is incremented too.
*
* It is safe to call this function from interrupt context.
*/
void pm_wakeup_event(struct device *dev, unsigned int msec)
{
unsigned long flags;
- struct delayed_work *dwork;
-
- dwork = msec ? kzalloc(sizeof(*dwork), GFP_ATOMIC) : NULL;
spin_lock_irqsave(&events_lock, flags);
+ event_count++;
if (dev)
dev->power.wakeup_count++;
- if (dwork) {
- INIT_DELAYED_WORK(dwork, pm_wakeup_work_fn);
- schedule_delayed_work(dwork, msecs_to_jiffies(msec));
+ if (msec) {
+ unsigned long expires;
- events_in_progress++;
- } else {
- event_count++;
+ expires = jiffies + msecs_to_jiffies(msec);
+ if (!expires)
+ expires = 1;
+
+ if (!events_timer_expires
+ || time_after(expires, events_timer_expires)) {
+ if (!events_timer_expires)
+ events_in_progress++;
+
+ mod_timer(&events_timer, expires);
+ events_timer_expires = expires;
+ }
}
spin_unlock_irqrestore(&events_lock, flags);
}
--
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