[PATCH] x86: slightly shorten __ticket_spin_trylock() (v3)

[Jan Beulich]

Since the callers generally expect a boolean value, there's no need to
zero-extend the outcome of the comparison. It just requires that all
of x86' trylock implementations have their return type changed
accordingly.

v2: Don't use bool for the return type though - this is being frowned
on and presently doesn't work with the pv-ops patching macros.

v3: Keep the return value in %eax (or really, %al).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>

---
 arch/x86/include/asm/paravirt.h       |    4 ++--
 arch/x86/include/asm/paravirt_types.h |    2 +-
 arch/x86/include/asm/spinlock.h       |   14 ++++++--------
 arch/x86/xen/spinlock.c               |    2 +-
 4 files changed, 10 insertions(+), 12 deletions(-)

--- linux-2.6.33-rc1/arch/x86/include/asm/paravirt.h	2009-12-18 16:05:40.000000000 +0100
+++ 2.6.33-rc1-x86-spin-trylock-simplify/arch/x86/include/asm/paravirt.h	2009-12-03 09:43:42.000000000 +0100
@@ -753,9 +753,9 @@ static __always_inline void arch_spin_lo
 	PVOP_VCALL2(pv_lock_ops.spin_lock_flags, lock, flags);
 }
 
-static __always_inline int arch_spin_trylock(struct arch_spinlock *lock)
+static __always_inline u8 arch_spin_trylock(struct arch_spinlock *lock)
 {
-	return PVOP_CALL1(int, pv_lock_ops.spin_trylock, lock);
+	return PVOP_CALL1(u8, pv_lock_ops.spin_trylock, lock);
 }
 
 static __always_inline void arch_spin_unlock(struct arch_spinlock *lock)
--- linux-2.6.33-rc1/arch/x86/include/asm/paravirt_types.h	2009-12-18 16:05:40.000000000 +0100
+++ 2.6.33-rc1-x86-spin-trylock-simplify/arch/x86/include/asm/paravirt_types.h	2009-12-03 09:43:50.000000000 +0100
@@ -324,7 +324,7 @@ struct pv_lock_ops {
 	int (*spin_is_contended)(struct arch_spinlock *lock);
 	void (*spin_lock)(struct arch_spinlock *lock);
 	void (*spin_lock_flags)(struct arch_spinlock *lock, unsigned long flags);
-	int (*spin_trylock)(struct arch_spinlock *lock);
+	u8 (*spin_trylock)(struct arch_spinlock *lock);
 	void (*spin_unlock)(struct arch_spinlock *lock);
 };
 
--- linux-2.6.33-rc1/arch/x86/include/asm/spinlock.h	2009-12-18 16:05:40.000000000 +0100
+++ 2.6.33-rc1-x86-spin-trylock-simplify/arch/x86/include/asm/spinlock.h	2009-12-10 15:30:52.000000000 +0100
@@ -77,7 +77,7 @@ static __always_inline void __ticket_spi
 		: "memory", "cc");
 }
 
-static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
+static __always_inline u8 __ticket_spin_trylock(arch_spinlock_t *lock)
 {
 	int tmp, new;
 
@@ -87,8 +87,7 @@ static __always_inline int __ticket_spin
 		     "jne 1f\n\t"
 		     LOCK_PREFIX "cmpxchgw %w1,%2\n\t"
 		     "1:"
-		     "sete %b1\n\t"
-		     "movzbl %b1,%0\n\t"
+		     "sete %b0\n\t"
 		     : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
 		     :
 		     : "memory", "cc");
@@ -127,7 +126,7 @@ static __always_inline void __ticket_spi
 		     : "memory", "cc");
 }
 
-static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
+static __always_inline u8 __ticket_spin_trylock(arch_spinlock_t *lock)
 {
 	int tmp;
 	int new;
@@ -140,9 +139,8 @@ static __always_inline int __ticket_spin
 		     "jne 1f\n\t"
 		     LOCK_PREFIX "cmpxchgl %1,%2\n\t"
 		     "1:"
-		     "sete %b1\n\t"
-		     "movzbl %b1,%0\n\t"
-		     : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
+		     "sete %b0\n\t"
+		     : "=&a" (tmp), "=&r" (new), "+m" (lock->slock)
 		     :
 		     : "memory", "cc");
 
@@ -190,7 +188,7 @@ static __always_inline void arch_spin_lo
 	__ticket_spin_lock(lock);
 }
 
-static __always_inline int arch_spin_trylock(arch_spinlock_t *lock)
+static __always_inline u8 arch_spin_trylock(arch_spinlock_t *lock)
 {
 	return __ticket_spin_trylock(lock);
 }
--- linux-2.6.33-rc1/arch/x86/xen/spinlock.c	2009-12-18 16:05:40.000000000 +0100
+++ 2.6.33-rc1-x86-spin-trylock-simplify/arch/x86/xen/spinlock.c	2009-12-03 09:44:33.000000000 +0100
@@ -136,7 +136,7 @@ static int xen_spin_is_contended(struct 
 	return xl->spinners != 0;
 }
 
-static int xen_spin_trylock(struct arch_spinlock *lock)
+static u8 xen_spin_trylock(struct arch_spinlock *lock)
 {
 	struct xen_spinlock *xl = (struct xen_spinlock *)lock;
 	u8 old = 1;


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