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Date: Mon, 21 Jul 2008 23:02:36 -0400
From: David Woodhouse <dwmw2@...radead.org>
To: linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
arjan@...radead.org
Subject: [RFC] Imprecise timers.
Many users of timers don't really care too much about exactly when their
timer fires -- and waking a CPU to satisfy such a timer is a waste of
power. This patch implements a 'range' timer which will fire at a 'convenient'
moment within given constraints.
It's implemented by a deferrable timer at the beginning of the range,
which will run some time later when the CPU happens to be awake. And a
non-deferrable timer at the hard deadline, to ensure it really does
happen by then.
Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
---
include/linux/timer.h | 101 ++++++++++++++++++++++++++++++++++++++++++++++++-
kernel/timer.c | 18 +++++---
2 files changed, 110 insertions(+), 9 deletions(-)
diff --git a/include/linux/timer.h b/include/linux/timer.h
index d4ba792..163137c 100644
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -23,22 +23,60 @@ struct timer_list {
#endif
};
+/* This can probably be optimised somehow, but for now we do it the
+ simple way: two timers, one deferrable and one for the deadline. */
+struct range_timer {
+ struct timer_list early;
+ struct timer_list deadline;
+ void (*function)(unsigned long);
+ unsigned long data;
+};
+
extern struct tvec_base boot_tvec_bases;
+/*
+ * Note that all tvec_bases are 2 byte aligned and lower bit of
+ * base in timer_list is guaranteed to be zero. Use the LSB for
+ * the new flag to indicate whether the timer is deferrable
+ */
+#define TBASE_DEFERRABLE_FLAG (0x1)
-#define TIMER_INITIALIZER(_function, _expires, _data) { \
+#define __TIMER_INITIALIZER(_function, _expires, _data, _base) {\
.entry = { .prev = TIMER_ENTRY_STATIC }, \
.function = (_function), \
.expires = (_expires), \
.data = (_data), \
- .base = &boot_tvec_bases, \
+ .base = (struct tvec_base *)(_base), \
}
+#define TIMER_INITIALIZER(_function, _expires, _data) \
+ __TIMER_INITIALIZER(_function, _expires, _data, &boot_tvec_bases)
+
+#define TIMER_INITIALIZER_DEFERRABLE(_function, _expires, _data) \
+ __TIMER_INITIALIZER(_function, _expires, _data, \
+ (unsigned long)&boot_tvec_bases + TBASE_DEFERRABLE_FLAG)
+
+void range_timer_func(unsigned long timer);
#define DEFINE_TIMER(_name, _function, _expires, _data) \
struct timer_list _name = \
TIMER_INITIALIZER(_function, _expires, _data)
+#define DEFINE_RANGE_TIMER(_name, _function, _expires, _deadline, _data)\
+ struct range_timer _name = { \
+ .early = TIMER_INITIALIZER_DEFERRABLE(range_timer_func, \
+ (_expires), (unsigned long)&(_name)), \
+ .deadline = TIMER_INITIALIZER(range_timer_func, \
+ (_deadline), (unsigned long)(&(_name))), \
+ .function = (_function), \
+ .data = (_data), \
+ }
+
void init_timer(struct timer_list *timer);
void init_timer_deferrable(struct timer_list *timer);
+static inline void init_range_timer(struct range_timer *timer)
+{
+ init_timer_deferrable(&timer->early);
+ init_timer(&timer->deadline);
+}
#ifdef CONFIG_DEBUG_OBJECTS_TIMERS
extern void init_timer_on_stack(struct timer_list *timer);
@@ -51,6 +89,19 @@ static inline void init_timer_on_stack(struct timer_list *timer)
}
#endif
+static inline void setup_range_timer(struct range_timer *timer,
+ void (*function)(unsigned long),
+ unsigned long data)
+{
+ timer->early.function = range_timer_func;
+ timer->early.data = (unsigned long)timer;
+ timer->deadline.function = range_timer_func;
+ timer->deadline.data = (unsigned long)timer;
+ timer->function = function;
+ timer->data = data;
+
+ init_range_timer(timer);
+}
static inline void setup_timer(struct timer_list * timer,
void (*function)(unsigned long),
unsigned long data)
@@ -83,12 +134,54 @@ static inline int timer_pending(const struct timer_list * timer)
{
return timer->entry.next != NULL;
}
+static inline int range_timer_pending(const struct range_timer *timer)
+{
+ return timer_pending(&timer->early) || timer_pending(&timer->deadline);
+}
extern void add_timer_on(struct timer_list *timer, int cpu);
extern int del_timer(struct timer_list * timer);
extern int __mod_timer(struct timer_list *timer, unsigned long expires);
extern int mod_timer(struct timer_list *timer, unsigned long expires);
+static inline void add_range_timer_on(struct range_timer *timer, int cpu)
+{
+ add_timer_on(&timer->early, cpu);
+ add_timer_on(&timer->deadline, cpu);
+}
+static inline int del_range_timer(struct range_timer *timer)
+{
+ return del_timer(&timer->early) | del_timer(&timer->deadline);
+}
+static inline int __mod_range_timer(struct range_timer *timer,
+ unsigned long expires,
+ unsigned long deadline)
+{
+ int ret;
+ WARN_ON(deadline < expires);
+ /* We need them on the same CPU */
+ preempt_disable();
+ ret = __mod_timer(&timer->early, expires);
+ ret |= __mod_timer(&timer->deadline, deadline);
+ preempt_enable();
+
+ return ret;
+}
+
+static inline int mod_range_timer(struct range_timer *timer,
+ unsigned long expires,
+ unsigned long deadline)
+{
+ int ret;
+ WARN_ON(deadline < expires);
+ /* We need them on the same CPU */
+ preempt_disable();
+ ret = mod_timer(&timer->early, expires);
+ ret |= mod_timer(&timer->deadline, deadline);
+ preempt_enable();
+
+ return ret;
+}
/*
* The jiffies value which is added to now, when there is no timer
* in the timer wheel:
@@ -174,6 +267,10 @@ static inline void add_timer(struct timer_list *timer)
# define del_timer_sync(t) del_timer(t)
#endif
+static inline int del_range_timer_sync(struct range_timer *timer)
+{
+ return del_timer_sync(&timer->early) | del_timer_sync(&timer->deadline);
+}
#define del_singleshot_timer_sync(t) del_timer_sync(t)
extern void init_timers(void);
diff --git a/kernel/timer.c b/kernel/timer.c
index 03bc7f1..e114f08 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -81,13 +81,6 @@ struct tvec_base boot_tvec_bases;
EXPORT_SYMBOL(boot_tvec_bases);
static DEFINE_PER_CPU(struct tvec_base *, tvec_bases) = &boot_tvec_bases;
-/*
- * Note that all tvec_bases are 2 byte aligned and lower bit of
- * base in timer_list is guaranteed to be zero. Use the LSB for
- * the new flag to indicate whether the timer is deferrable
- */
-#define TBASE_DEFERRABLE_FLAG (0x1)
-
/* Functions below help us manage 'deferrable' flag */
static inline unsigned int tbase_get_deferrable(struct tvec_base *base)
{
@@ -1525,3 +1518,14 @@ unsigned long msleep_interruptible(unsigned int msecs)
}
EXPORT_SYMBOL(msleep_interruptible);
+
+void range_timer_func(unsigned long t)
+{
+ struct range_timer *timer = (void *)t;
+
+ del_timer(&timer->early);
+ del_timer(&timer->deadline);
+
+ timer->function(timer->data);
+}
+EXPORT_SYMBOL_GPL(range_timer_func);
--
1.5.5.1
--
David Woodhouse Open Source Technology Centre
David.Woodhouse@...el.com Intel Corporation
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