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SubjectRe: [patch] 2.4.4 alpha semaphores optimization
On Fri, May 04, 2001 at 10:22:53AM +0100, David Howells wrote:
> I don't know whether it will (a) compile, or (b) work... I don't have an alpha
> to play with.

Neither (a) nor (b) ;-) Corrected asm-alpha/rwsem.h attached.
Also small fix for lib/rwsem.c -- RWSEM_WAITING_BIAS-RWSEM_ACTIVE_BIAS
won't fit in the __s32 if counters are 64-bit.

--- linux/lib/rwsem.c.orig Sat Apr 28 00:58:28 2001
+++ linux/lib/rwsem.c Fri May 4 17:38:06 2001
@@ -112,7 +112,7 @@ static inline struct rw_semaphore *__rws
*/
static inline struct rw_semaphore *rwsem_down_failed_common(struct rw_semaphore *sem,
struct rwsem_waiter *waiter,
- __s32 adjustment)
+ signed long adjustment)
{
struct task_struct *tsk = current;
signed long count;
Ivan.

#ifndef _ALPHA_RWSEM_H
#define _ALPHA_RWSEM_H

/*
* Written by Ivan Kokshaysky <ink@jurassic.park.msu.ru>, 2001.
* Based on asm-alpha/semaphore.h and asm-i386/rwsem.h
*/

#ifndef _LINUX_RWSEM_H
#error please dont include asm/rwsem.h directly, use linux/rwsem.h instead
#endif

#ifdef __KERNEL__

#include <linux/list.h>
#include <linux/spinlock.h>

struct rwsem_waiter;

extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);

/*
* the semaphore definition
*/
struct rw_semaphore {
long count;
#define RWSEM_UNLOCKED_VALUE 0x0000000000000000L
#define RWSEM_ACTIVE_BIAS 0x0000000000000001L
#define RWSEM_ACTIVE_MASK 0x00000000ffffffffL
#define RWSEM_WAITING_BIAS (-0x0000000100000000L)
#define RWSEM_ACTIVE_READ_BIAS RWSEM_ACTIVE_BIAS
#define RWSEM_ACTIVE_WRITE_BIAS (RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
spinlock_t wait_lock;
struct list_head wait_list;
#if RWSEM_DEBUG
int debug;
#endif
};

#if RWSEM_DEBUG
#define __RWSEM_DEBUG_INIT , 0
#else
#define __RWSEM_DEBUG_INIT /* */
#endif

#define __RWSEM_INITIALIZER(name) \
{ RWSEM_UNLOCKED_VALUE, SPIN_LOCK_UNLOCKED, \
LIST_HEAD_INIT((name).wait_list) __RWSEM_DEBUG_INIT }

#define DECLARE_RWSEM(name) \
struct rw_semaphore name = __RWSEM_INITIALIZER(name)

static inline void init_rwsem(struct rw_semaphore *sem)
{
sem->count = RWSEM_UNLOCKED_VALUE;
spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
#if RWSEM_DEBUG
sem->debug = 0;
#endif
}

static inline void __down_read(struct rw_semaphore *sem)
{
long oldcount, temp;
__asm__ __volatile__(
"1: ldq_l %0,%1\n"
" addq %0,%3,%2\n"
" stq_c %2,%1\n"
" beq %2,2f\n"
#ifdef CONFIG_SMP
" mb\n"
#endif
".subsection 2\n"
"2: br 1b\n"
".previous"
:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
:"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");

if (oldcount < 0)
rwsem_down_read_failed(sem);
}

static inline void __down_write(struct rw_semaphore *sem)
{
long granted, temp;
__asm__ __volatile__(
"1: ldq_l %0,%1\n"
" addq %0,%3,%2\n"
" stq_c %2,%1\n"
" beq %2,2f\n"
#ifdef CONFIG_SMP
" mb\n"
#endif
" cmpeq %0,0,%0\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
:"=&r" (granted), "=m" (sem->count), "=&r" (temp)
:"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");

if (!granted)
rwsem_down_write_failed(sem);
}

static inline void __up_read(struct rw_semaphore *sem)
{
long oldcount, temp;
__asm__ __volatile__(
#ifdef CONFIG_SMP
" mb\n"
#endif
"1: ldq_l %0,%1\n"
" subq %0,%3,%2\n"
" stq_c %2,%1\n"
" beq %2,2f\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
:"=&r" (oldcount), "=m" (sem->count), "=&r" (temp)
:"Ir" (RWSEM_ACTIVE_READ_BIAS), "m" (sem->count) : "memory");

if (oldcount < 0)
if ((oldcount & RWSEM_ACTIVE_MASK) == 0)
rwsem_wake(sem);
}

static inline void __up_write(struct rw_semaphore *sem)
{
long count, cmp;
__asm__ __volatile__(
#ifdef CONFIG_SMP
" mb\n"
#endif
"1: ldq_l %0,%1\n"
" subq %0,%3,%2\n"
" stq_c %2,%1\n"
" beq %2,2f\n"
" cmpeq %0,%3,%2\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
:"=&r" (count), "=m" (sem->count), "=&r" (cmp)
:"Ir" (RWSEM_ACTIVE_WRITE_BIAS), "m" (sem->count) : "memory");

if (!cmp)
if ((int)count - RWSEM_ACTIVE_BIAS == 0)
rwsem_wake(sem);
}

static inline void rwsem_atomic_add(long val, struct rw_semaphore *sem)
{
long temp;
__asm__ __volatile__(
"1: ldq_l %0,%1\n"
" addq %0,%2,%0\n"
" stq_c %0,%1\n"
" beq %0,2f\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
:"=&r" (temp), "=m" (sem->count)
:"Ir" (val), "m" (sem->count));
}

static inline long rwsem_atomic_update(long val, struct rw_semaphore *sem)
{
long temp, ret;
__asm__ __volatile__(
"1: ldq_l %0,%1\n"
" addq %0,%3,%2\n"
" addq %0,%3,%0\n"
" stq_c %2,%1\n"
" beq %2,2f\n"
".subsection 2\n"
"2: br 1b\n"
".previous"
:"=&r" (ret), "=m" (sem->count), "=&r" (temp)
:"Ir" (val), "m" (sem->count));

return ret;
}

#endif /* __KERNEL__ */
#endif /* _ALPHA_RWSEM_H */
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