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#ifndef __LINUX_BRLOCK_H
#define __LINUX_BRLOCK_H
/*
* 'Big Reader' read-write spinlocks.
*
* super-fast read/write locks, with write-side penalty. The point
* is to have a per-CPU read/write lock. Readers lock their CPU-local
* readlock, writers must lock all locks to get write access. These
* CPU-read-write locks are semantically identical to normal rwlocks.
* Memory usage is higher as well. (NR_CPUS*L1_CACHE_BYTES bytes)
*
* The most important feature is that these spinlocks do not cause
* cacheline ping-pong in the 'most readonly data' case.
*
* Copyright 2000, Ingo Molnar <mingo@redhat.com>
*
* Registry idea and naming [ crutial! :-) ] by:
*
* David S. Miller <davem@redhat.com>
*
* David has an implementation that doesnt use atomic operations in
* the read branch via memory ordering tricks - i guess we need to
* split this up into a per-arch thing? The atomicity issue is a
* secondary item in profiles, at least on x86 platforms.
*
* The atomic op version overhead is indeed a big deal on
* load-locked/store-conditional cpus (ALPHA/MIPS/PPC) and
* compare-and-swap cpus (Sparc64). So we control which
* implementation to use with a __BRLOCK_USE_ATOMICS define. -DaveM
*/
/* Register bigreader lock indices here. */
enum brlock_indices {
BR_GLOBALIRQ_LOCK,
BR_NETPROTO_LOCK,
__BR_END
};
#include <linux/config.h>
#ifdef CONFIG_SMP
#include <linux/cache.h>
#include <linux/spinlock.h>
#if defined(__i386__) || defined(__ia64__) || defined(__x86_64__)
#define __BRLOCK_USE_ATOMICS
#else
#undef __BRLOCK_USE_ATOMICS
#endif
#ifdef __BRLOCK_USE_ATOMICS
typedef rwlock_t brlock_read_lock_t;
#else
typedef unsigned int brlock_read_lock_t;
#endif
/*
* align last allocated index to the next cacheline:
*/
#define __BR_IDX_MAX \
(((sizeof(brlock_read_lock_t)*__BR_END + SMP_CACHE_BYTES-1) & ~(SMP_CACHE_BYTES-1)) / sizeof(brlock_read_lock_t))
extern brlock_read_lock_t __brlock_array[NR_CPUS][__BR_IDX_MAX];
#ifndef __BRLOCK_USE_ATOMICS
struct br_wrlock {
spinlock_t lock;
} __attribute__ ((__aligned__(SMP_CACHE_BYTES)));
extern struct br_wrlock __br_write_locks[__BR_IDX_MAX];
#endif
extern void __br_lock_usage_bug (void);
#ifdef __BRLOCK_USE_ATOMICS
static inline void br_read_lock (enum brlock_indices idx)
{
/*
* This causes a link-time bug message if an
* invalid index is used:
*/
if (idx >= __BR_END)
__br_lock_usage_bug();
read_lock(&__brlock_array[smp_processor_id()][idx]);
}
static inline void br_read_unlock (enum brlock_indices idx)
{
if (idx >= __BR_END)
__br_lock_usage_bug();
read_unlock(&__brlock_array[smp_processor_id()][idx]);
}
#else /* ! __BRLOCK_USE_ATOMICS */
static inline void br_read_lock (enum brlock_indices idx)
{
unsigned int *ctr;
spinlock_t *lock;
/*
* This causes a link-time bug message if an
* invalid index is used:
*/
if (idx >= __BR_END)
__br_lock_usage_bug();
ctr = &__brlock_array[smp_processor_id()][idx];
lock = &__br_write_locks[idx].lock;
again:
(*ctr)++;
mb();
if (spin_is_locked(lock)) {
(*ctr)--;
wmb(); /*
* The release of the ctr must become visible
* to the other cpus eventually thus wmb(),
* we don't care if spin_is_locked is reordered
* before the releasing of the ctr.
* However IMHO this wmb() is superflous even in theory.
* It would not be superflous only if on the
* other CPUs doing a ldl_l instead of an ldl
* would make a difference and I don't think this is
* the case.
* I'd like to clarify this issue further
* but for now this is a slow path so adding the
* wmb() will keep us on the safe side.
*/
while (spin_is_locked(lock))
barrier();
goto again;
}
}
static inline void br_read_unlock (enum brlock_indices idx)
{
unsigned int *ctr;
if (idx >= __BR_END)
__br_lock_usage_bug();
ctr = &__brlock_array[smp_processor_id()][idx];
wmb();
(*ctr)--;
}
#endif /* __BRLOCK_USE_ATOMICS */
/* write path not inlined - it's rare and larger */
extern void FASTCALL(__br_write_lock (enum brlock_indices idx));
extern void FASTCALL(__br_write_unlock (enum brlock_indices idx));
static inline void br_write_lock (enum brlock_indices idx)
{
if (idx >= __BR_END)
__br_lock_usage_bug();
__br_write_lock(idx);
}
static inline void br_write_unlock (enum brlock_indices idx)
{
if (idx >= __BR_END)
__br_lock_usage_bug();
__br_write_unlock(idx);
}
#else
# define br_read_lock(idx) ((void)(idx))
# define br_read_unlock(idx) ((void)(idx))
# define br_write_lock(idx) ((void)(idx))
# define br_write_unlock(idx) ((void)(idx))
#endif
/*
* Now enumerate all of the possible sw/hw IRQ protected
* versions of the interfaces.
*/
#define br_read_lock_irqsave(idx, flags) \
do { local_irq_save(flags); br_read_lock(idx); } while (0)
#define br_read_lock_irq(idx) \
do { local_irq_disable(); br_read_lock(idx); } while (0)
#define br_read_lock_bh(idx) \
do { local_bh_disable(); br_read_lock(idx); } while (0)
#define br_write_lock_irqsave(idx, flags) \
do { local_irq_save(flags); br_write_lock(idx); } while (0)
#define br_write_lock_irq(idx) \
do { local_irq_disable(); br_write_lock(idx); } while (0)
#define br_write_lock_bh(idx) \
do { local_bh_disable(); br_write_lock(idx); } while (0)
#define br_read_unlock_irqrestore(idx, flags) \
do { br_read_unlock(irx); local_irq_restore(flags); } while (0)
#define br_read_unlock_irq(idx) \
do { br_read_unlock(idx); local_irq_enable(); } while (0)
#define br_read_unlock_bh(idx) \
do { br_read_unlock(idx); local_bh_enable(); } while (0)
#define br_write_unlock_irqrestore(idx, flags) \
do { br_write_unlock(irx); local_irq_restore(flags); } while (0)
#define br_write_unlock_irq(idx) \
do { br_write_unlock(idx); local_irq_enable(); } while (0)
#define br_write_unlock_bh(idx) \
do { br_write_unlock(idx); local_bh_enable(); } while (0)
#endif /* __LINUX_BRLOCK_H */
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