ef6edc9746
On systems running with virtual cpus there is optimization potential in regard to spinlocks and rw-locks. If the virtual cpu that has taken a lock is known to a cpu that wants to acquire the same lock it is beneficial to yield the timeslice of the virtual cpu in favour of the cpu that has the lock (directed yield). With CONFIG_PREEMPT="n" this can be implemented by the architecture without common code changes. Powerpc already does this. With CONFIG_PREEMPT="y" the lock loops are coded with _raw_spin_trylock, _raw_read_trylock and _raw_write_trylock in kernel/spinlock.c. If the lock could not be taken cpu_relax is called. A directed yield is not possible because cpu_relax doesn't know anything about the lock. To be able to yield the lock in favour of the current lock holder variants of cpu_relax for spinlocks and rw-locks are needed. The new _raw_spin_relax, _raw_read_relax and _raw_write_relax primitives differ from cpu_relax insofar that they have an argument: a pointer to the lock structure. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Paul Mackerras <paulus@samba.org> Cc: Haavard Skinnemoen <hskinnemoen@atmel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
108 lines
2.4 KiB
C
108 lines
2.4 KiB
C
/*
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* include/asm-sh/spinlock.h
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*
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* Copyright (C) 2002, 2003 Paul Mundt
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file "COPYING" in the main directory of this archive
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* for more details.
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*/
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#ifndef __ASM_SH_SPINLOCK_H
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#define __ASM_SH_SPINLOCK_H
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#include <asm/atomic.h>
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/*
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* Your basic SMP spinlocks, allowing only a single CPU anywhere
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*/
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#define __raw_spin_is_locked(x) ((x)->lock != 0)
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#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
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#define __raw_spin_unlock_wait(x) \
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do { cpu_relax(); } while (__raw_spin_is_locked(x))
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/*
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* Simple spin lock operations. There are two variants, one clears IRQ's
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* on the local processor, one does not.
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*
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* We make no fairness assumptions. They have a cost.
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*/
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static inline void __raw_spin_lock(raw_spinlock_t *lock)
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{
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__asm__ __volatile__ (
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"1:\n\t"
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"tas.b @%0\n\t"
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"bf/s 1b\n\t"
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"nop\n\t"
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: "=r" (lock->lock)
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: "r" (&lock->lock)
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: "t", "memory"
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);
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}
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static inline void __raw_spin_unlock(raw_spinlock_t *lock)
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{
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assert_spin_locked(lock);
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lock->lock = 0;
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}
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#define __raw_spin_trylock(x) (!test_and_set_bit(0, &(x)->lock))
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/*
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* Read-write spinlocks, allowing multiple readers but only one writer.
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*
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* NOTE! it is quite common to have readers in interrupts but no interrupt
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* writers. For those circumstances we can "mix" irq-safe locks - any writer
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* needs to get a irq-safe write-lock, but readers can get non-irqsafe
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* read-locks.
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*/
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static inline void __raw_read_lock(raw_rwlock_t *rw)
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{
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__raw_spin_lock(&rw->lock);
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atomic_inc(&rw->counter);
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__raw_spin_unlock(&rw->lock);
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}
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static inline void __raw_read_unlock(raw_rwlock_t *rw)
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{
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__raw_spin_lock(&rw->lock);
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atomic_dec(&rw->counter);
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__raw_spin_unlock(&rw->lock);
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}
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static inline void __raw_write_lock(raw_rwlock_t *rw)
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{
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__raw_spin_lock(&rw->lock);
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atomic_set(&rw->counter, -1);
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}
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static inline void __raw_write_unlock(raw_rwlock_t *rw)
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{
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atomic_set(&rw->counter, 0);
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__raw_spin_unlock(&rw->lock);
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}
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#define __raw_read_trylock(lock) generic__raw_read_trylock(lock)
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static inline int __raw_write_trylock(raw_rwlock_t *rw)
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{
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if (atomic_sub_and_test(RW_LOCK_BIAS, &rw->counter))
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return 1;
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atomic_add(RW_LOCK_BIAS, &rw->counter);
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return 0;
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}
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#define _raw_spin_relax(lock) cpu_relax()
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#define _raw_read_relax(lock) cpu_relax()
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#define _raw_write_relax(lock) cpu_relax()
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#endif /* __ASM_SH_SPINLOCK_H */
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