On Sun, 2013-06-09 at 12:36 -0700, Paul E. McKenney wrote:
>
> +#else /* #ifndef CONFIG_TICKET_LOCK_QUEUED */
> +
> +bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc);
> +
> +static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
> +{
> + register struct __raw_tickets inc = { .tail = 2 };
> +
> + inc = xadd(&lock->tickets, inc);
> + for (;;) {
> + if (inc.head == inc.tail || tkt_spin_pass(lock, inc))
> + break;
> + inc.head = ACCESS_ONCE(lock->tickets.head);
> + }
> + barrier(); /* smp_mb() on Power or ARM. */
> +}
> +
> +#endif /* #else #ifndef CONFIG_TICKET_LOCK_QUEUED */
> +
To avoid the above code duplication, I would have this instead:
#ifdef CONFIG_TICKET_LOCK_QUEUED
bool tkt_spin_pass(arch_spinlock_t *ap, struct __raw_tickets inc);
#define __TKT_SPIN_INC 2
#else
static inline bool tkt_spin_pass(arch_spinlock_t *ap, struct
__raw_tickets inc)
{
return false;
}
#define __TKT_SPIN_INC 1
#endif
static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
{
register struct __raw_tickets inc = { .tail = __TKT_SPIN_INC };
inc = xadd(&lock->tickets, inc);
for (;;) {
if (inc.head == inc.tail || tkt_spin_pass(lock, inc))
break;
cpu_relax();
inc.head = ACCESS_ONCE(lock->tickets.head);
}
barrier; /* make sure nothing creeps before the lock is taken */
}
-- Steve
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