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Commit afb33f8c authored by Jiri Kosina's avatar Jiri Kosina Committed by Ingo Molnar
Browse files

x86: remove byte locks 



Impact: cleanup

Remove byte locks implementation, which was introduced by Jeremy in
8efcbab6 ("paravirt: introduce a "lock-byte" spinlock implementation"),
but turned out to be dead code that is not used by any in-kernel
virtualization guest (Xen uses its own variant of spinlocks implementation
and KVM is not planning to move to byte locks).

Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 422e79a8

arch/x86/include/asm/paravirt.h

+0 −2
Original line number Diff line number Diff line
@@ -1389,8 +1389,6 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx, 
void _paravirt_nop(void);

#define paravirt_nop	((void *)_paravirt_nop)



void paravirt_use_bytelocks(void);



#ifdef CONFIG_SMP



static inline int __raw_spin_is_locked(struct raw_spinlock *lock)

arch/x86/include/asm/spinlock.h

+2 −64
Original line number Diff line number Diff line
@@ -172,70 +172,8 @@ static inline int __ticket_spin_is_contended(raw_spinlock_t *lock) 
	return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;

}



#ifdef CONFIG_PARAVIRT

/*

 * Define virtualization-friendly old-style lock byte lock, for use in

 * pv_lock_ops if desired.

 *

 * This differs from the pre-2.6.24 spinlock by always using xchgb

 * rather than decb to take the lock; this allows it to use a

 * zero-initialized lock structure.  It also maintains a 1-byte

 * contention counter, so that we can implement

 * __byte_spin_is_contended.

 */

struct __byte_spinlock {

	s8 lock;

	s8 spinners;

};



static inline int __byte_spin_is_locked(raw_spinlock_t *lock)

{

	struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;

	return bl->lock != 0;

}

#ifndef CONFIG_PARAVIRT



static inline int __byte_spin_is_contended(raw_spinlock_t *lock)

{

	struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;

	return bl->spinners != 0;

}



static inline void __byte_spin_lock(raw_spinlock_t *lock)

{

	struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;

	s8 val = 1;



	asm("1: xchgb %1, %0\n"

	    "   test %1,%1\n"

	    "   jz 3f\n"

	    "   " LOCK_PREFIX "incb %2\n"

	    "2: rep;nop\n"

	    "   cmpb $1, %0\n"

	    "   je 2b\n"

	    "   " LOCK_PREFIX "decb %2\n"

	    "   jmp 1b\n"

	    "3:"

	    : "+m" (bl->lock), "+q" (val), "+m" (bl->spinners): : "memory");

}



static inline int __byte_spin_trylock(raw_spinlock_t *lock)

{

	struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;

	u8 old = 1;



	asm("xchgb %1,%0"

	    : "+m" (bl->lock), "+q" (old) : : "memory");



	return old == 0;

}



static inline void __byte_spin_unlock(raw_spinlock_t *lock)

{

	struct __byte_spinlock *bl = (struct __byte_spinlock *)lock;

	smp_wmb();

	bl->lock = 0;

}

#else  /* !CONFIG_PARAVIRT */

static inline int __raw_spin_is_locked(raw_spinlock_t *lock)

{

	return __ticket_spin_is_locked(lock);
@@ -267,7 +205,7 @@ static __always_inline void __raw_spin_lock_flags(raw_spinlock_t *lock, 
	__raw_spin_lock(lock);

}



#endif	/* CONFIG_PARAVIRT */

#endif



static inline void __raw_spin_unlock_wait(raw_spinlock_t *lock)

{

arch/x86/kernel/paravirt-spinlocks.c

+0 −10
Original line number Diff line number Diff line
@@ -26,13 +26,3 @@ struct pv_lock_ops pv_lock_ops = { 
};

EXPORT_SYMBOL(pv_lock_ops);

void __init paravirt_use_bytelocks(void)

{

#ifdef CONFIG_SMP

	pv_lock_ops.spin_is_locked = __byte_spin_is_locked;

	pv_lock_ops.spin_is_contended = __byte_spin_is_contended;

	pv_lock_ops.spin_lock = __byte_spin_lock;

	pv_lock_ops.spin_trylock = __byte_spin_trylock;

	pv_lock_ops.spin_unlock = __byte_spin_unlock;

#endif

}