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>
173 lines
3.1 KiB
C
173 lines
3.1 KiB
C
#ifndef _ALPHA_SPINLOCK_H
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#define _ALPHA_SPINLOCK_H
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#include <asm/system.h>
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#include <linux/kernel.h>
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#include <asm/current.h>
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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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#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
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#define __raw_spin_is_locked(x) ((x)->lock != 0)
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#define __raw_spin_unlock_wait(x) \
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do { cpu_relax(); } while ((x)->lock)
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static inline void __raw_spin_unlock(raw_spinlock_t * lock)
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{
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mb();
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lock->lock = 0;
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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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long tmp;
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__asm__ __volatile__(
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"1: ldl_l %0,%1\n"
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" bne %0,2f\n"
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" lda %0,1\n"
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" stl_c %0,%1\n"
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" beq %0,2f\n"
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" mb\n"
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".subsection 2\n"
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"2: ldl %0,%1\n"
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" bne %0,2b\n"
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" br 1b\n"
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".previous"
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: "=&r" (tmp), "=m" (lock->lock)
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: "m"(lock->lock) : "memory");
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}
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static inline int __raw_spin_trylock(raw_spinlock_t *lock)
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{
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return !test_and_set_bit(0, &lock->lock);
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}
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/***********************************************************/
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static inline int __raw_read_can_lock(raw_rwlock_t *lock)
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{
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return (lock->lock & 1) == 0;
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}
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static inline int __raw_write_can_lock(raw_rwlock_t *lock)
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{
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return lock->lock == 0;
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}
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static inline void __raw_read_lock(raw_rwlock_t *lock)
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{
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long regx;
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__asm__ __volatile__(
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"1: ldl_l %1,%0\n"
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" blbs %1,6f\n"
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" subl %1,2,%1\n"
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" stl_c %1,%0\n"
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" beq %1,6f\n"
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" mb\n"
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".subsection 2\n"
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"6: ldl %1,%0\n"
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" blbs %1,6b\n"
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" br 1b\n"
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".previous"
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: "=m" (*lock), "=&r" (regx)
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: "m" (*lock) : "memory");
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}
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static inline void __raw_write_lock(raw_rwlock_t *lock)
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{
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long regx;
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__asm__ __volatile__(
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"1: ldl_l %1,%0\n"
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" bne %1,6f\n"
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" lda %1,1\n"
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" stl_c %1,%0\n"
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" beq %1,6f\n"
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" mb\n"
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".subsection 2\n"
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"6: ldl %1,%0\n"
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" bne %1,6b\n"
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" br 1b\n"
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".previous"
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: "=m" (*lock), "=&r" (regx)
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: "m" (*lock) : "memory");
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}
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static inline int __raw_read_trylock(raw_rwlock_t * lock)
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{
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long regx;
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int success;
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__asm__ __volatile__(
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"1: ldl_l %1,%0\n"
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" lda %2,0\n"
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" blbs %1,2f\n"
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" subl %1,2,%2\n"
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" stl_c %2,%0\n"
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" beq %2,6f\n"
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"2: mb\n"
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".subsection 2\n"
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"6: br 1b\n"
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".previous"
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: "=m" (*lock), "=&r" (regx), "=&r" (success)
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: "m" (*lock) : "memory");
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return success;
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}
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static inline int __raw_write_trylock(raw_rwlock_t * lock)
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{
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long regx;
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int success;
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__asm__ __volatile__(
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"1: ldl_l %1,%0\n"
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" lda %2,0\n"
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" bne %1,2f\n"
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" lda %2,1\n"
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" stl_c %2,%0\n"
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" beq %2,6f\n"
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"2: mb\n"
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".subsection 2\n"
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"6: br 1b\n"
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".previous"
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: "=m" (*lock), "=&r" (regx), "=&r" (success)
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: "m" (*lock) : "memory");
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return success;
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}
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static inline void __raw_read_unlock(raw_rwlock_t * lock)
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{
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long regx;
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__asm__ __volatile__(
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" mb\n"
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"1: ldl_l %1,%0\n"
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" addl %1,2,%1\n"
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" stl_c %1,%0\n"
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" beq %1,6f\n"
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".subsection 2\n"
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"6: br 1b\n"
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".previous"
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: "=m" (*lock), "=&r" (regx)
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: "m" (*lock) : "memory");
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}
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static inline void __raw_write_unlock(raw_rwlock_t * lock)
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{
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mb();
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lock->lock = 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 /* _ALPHA_SPINLOCK_H */
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