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spinlock: lockbreak cleanup

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The break_lock data structure and code for spinlocks is quite nasty.
Not only does it double the size of a spinlock but it changes locking to
a potentially less optimal trylock.

Put all of that under CONFIG_GENERIC_LOCKBREAK, and introduce a
__raw_spin_is_contended that uses the lock data itself to determine whether
there are waiters on the lock, to be used if CONFIG_GENERIC_LOCKBREAK is
not set.

Rename need_lockbreak to spin_needbreak, make it use spin_is_contended to
decouple it from the spinlock implementation, and make it typesafe (rwlocks
do not have any need_lockbreak sites -- why do they even get bloated up
with that break_lock then?).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Nick Piggin 2008-01-30 13:31:20 +01:00 • committed by Ingo Molnar
commit 95c354fe9f
19 changed files with 72 additions and 37 deletions
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21
include/linux/sched.h
View file

@ -1922,23 +1922,16 @@ extern int cond_resched_softirq(void);
/*
* Does a critical section need to be broken due to another
* task waiting?:
* task waiting?: (technically does not depend on CONFIG_PREEMPT,
* but a general need for low latency)
*/
#if defined(CONFIG_PREEMPT) && defined(CONFIG_SMP)
# define need_lockbreak(lock) ((lock)->break_lock)
#else
# define need_lockbreak(lock) 0
#endif
/*
* Does a critical section need to be broken due to another
* task waiting or preemption being signalled:
*/
static inline int lock_need_resched(spinlock_t *lock)
static inline int spin_needbreak(spinlock_t *lock)
{
if (need_lockbreak(lock) || need_resched())
return 1;
#ifdef CONFIG_PREEMPT
return spin_is_contended(lock);
#else
return 0;
#endif
}
/*