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timer: Permit statically-declared work with deferrable timers

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Currently, you have to just define a delayed_work uninitialised, and then
initialise it before first use.  That's a tad clumsy.  At risk of playing
mind-games with the compiler, fooling it into doing pointer arithmetic
with compile-time-constants, this lets clients properly initialise delayed
work with deferrable timers statically.

This patch was inspired by the issues which lead Artem Bityutskiy to
commit 8eab945c56 ("sunrpc: make the cache cleaner workqueue
deferrable").

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
Acked-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Phil Carmody 2010-10-20 15:57:33 -07:00 committed by Thomas Gleixner
parent 2bf1c05e3c
commit dd6414b50f
3 changed files with 34 additions and 14 deletions
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25
include/linux/timer.h
View file

@ -48,6 +48,18 @@ extern struct tvec_base boot_tvec_bases;
#define __TIMER_LOCKDEP_MAP_INITIALIZER(_kn)
#endif
/*
* 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 to
* indicate whether the timer is deferrable.
*
* A deferrable timer will work normally when the system is busy, but
* will not cause a CPU to come out of idle just to service it; instead,
* the timer will be serviced when the CPU eventually wakes up with a
* subsequent non-deferrable timer.
*/
#define TBASE_DEFERRABLE_FLAG (0x1)
#define TIMER_INITIALIZER(_function, _expires, _data) { \
.entry = { .prev = TIMER_ENTRY_STATIC }, \
.function = (_function), \
@ -59,6 +71,19 @@ extern struct tvec_base boot_tvec_bases;
__FILE__ ":" __stringify(__LINE__)) \
}
#define TBASE_MAKE_DEFERRED(ptr) ((struct tvec_base *) \
((unsigned char *)(ptr) + TBASE_DEFERRABLE_FLAG))
#define TIMER_DEFERRED_INITIALIZER(_function, _expires, _data) {\
.entry = { .prev = TIMER_ENTRY_STATIC }, \
.function = (_function), \
.expires = (_expires), \
.data = (_data), \
.base = TBASE_MAKE_DEFERRED(&boot_tvec_bases), \
__TIMER_LOCKDEP_MAP_INITIALIZER( \
__FILE__ ":" __stringify(__LINE__)) \
}
#define DEFINE_TIMER(_name, _function, _expires, _data) \
struct timer_list _name = \
TIMER_INITIALIZER(_function, _expires, _data)

8
include/linux/workqueue.h
View file

@ -127,12 +127,20 @@ struct execute_work {
.timer = TIMER_INITIALIZER(NULL, 0, 0), \
}
#define __DEFERRED_WORK_INITIALIZER(n, f) { \
.work = __WORK_INITIALIZER((n).work, (f)), \
.timer = TIMER_DEFERRED_INITIALIZER(NULL, 0, 0), \
}
#define DECLARE_WORK(n, f) \
struct work_struct n = __WORK_INITIALIZER(n, f)
#define DECLARE_DELAYED_WORK(n, f) \
struct delayed_work n = __DELAYED_WORK_INITIALIZER(n, f)
#define DECLARE_DEFERRED_WORK(n, f) \
struct delayed_work n = __DEFERRED_WORK_INITIALIZER(n, f)
/*
* initialize a work item's function pointer
*/

15
kernel/timer.c
View file

@ -88,18 +88,6 @@ 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 to
* indicate whether the timer is deferrable.
*
* A deferrable timer will work normally when the system is busy, but
* will not cause a CPU to come out of idle just to service it; instead,
* the timer will be serviced when the CPU eventually wakes up with a
* subsequent non-deferrable timer.
*/
#define TBASE_DEFERRABLE_FLAG (0x1)
/* Functions below help us manage 'deferrable' flag */
static inline unsigned int tbase_get_deferrable(struct tvec_base *base)
{
@ -113,8 +101,7 @@ static inline struct tvec_base *tbase_get_base(struct tvec_base *base)
static inline void timer_set_deferrable(struct timer_list *timer)
{
timer->base = ((struct tvec_base *)((unsigned long)(timer->base) |
TBASE_DEFERRABLE_FLAG));
timer->base = TBASE_MAKE_DEFERRED(timer->base);
}
static inline void