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Subject[PATCH 6/8] x86/ticketlock: make __ticket_spin_trylock common
Date
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

Make trylock code common regardless of ticket size.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
arch/x86/include/asm/spinlock.h | 49 +++++++--------------------------
arch/x86/include/asm/spinlock_types.h | 6 +++-
2 files changed, 14 insertions(+), 41 deletions(-)
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 0b8d2b2..dac6fc6 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -98,48 +98,19 @@ static __always_inline void __ticket_spin_lock(struct arch_spinlock *lock)
out: barrier(); /* make sure nothing creeps before the lock is taken */
}

-#if (NR_CPUS < 256)
static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
{
- unsigned int tmp, new;
-
- asm volatile("movzwl %2, %0\n\t"
- "cmpb %h0,%b0\n\t"
- "leal 0x100(%" REG_PTR_MODE "0), %1\n\t"
- "jne 1f\n\t"
- LOCK_PREFIX "cmpxchgw %w1,%2\n\t"
- "1:"
- "sete %b1\n\t"
- "movzbl %b1,%0\n\t"
- : "=&a" (tmp), "=&q" (new), "+m" (lock->slock)
- :
- : "memory", "cc");
-
- return tmp;
-}
-#else
-static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
-{
- unsigned tmp;
- unsigned new;
-
- asm volatile("movl %2,%0\n\t"
- "movl %0,%1\n\t"
- "roll $16, %0\n\t"
- "cmpl %0,%1\n\t"
- "leal 0x00010000(%" REG_PTR_MODE "0), %1\n\t"
- "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)
- :
- : "memory", "cc");
-
- return tmp;
+ arch_spinlock_t old, new;
+
+ old.tickets = ACCESS_ONCE(lock->tickets);
+ if (old.tickets.head != old.tickets.tail)
+ return 0;
+
+ new.head_tail = old.head_tail + (1 << TICKET_SHIFT);
+
+ /* cmpxchg is a full barrier, so nothing can move before it */
+ return cmpxchg(&lock->head_tail, old.head_tail, new.head_tail) == old.head_tail;
}
-#endif

static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
{
diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
index e3ad1e3..72e154e 100644
--- a/arch/x86/include/asm/spinlock_types.h
+++ b/arch/x86/include/asm/spinlock_types.h
@@ -9,8 +9,10 @@

#if (CONFIG_NR_CPUS < 256)
typedef u8 __ticket_t;
+typedef u16 __ticketpair_t;
#else
typedef u16 __ticket_t;
+typedef u32 __ticketpair_t;
#endif

#define TICKET_SHIFT (sizeof(__ticket_t) * 8)
@@ -18,14 +20,14 @@ typedef u16 __ticket_t;

typedef struct arch_spinlock {
union {
- unsigned int slock;
+ __ticketpair_t head_tail;
struct __raw_tickets {
__ticket_t head, tail;
} tickets;
};
} arch_spinlock_t;

-#define __ARCH_SPIN_LOCK_UNLOCKED { { .slock = 0 } }
+#define __ARCH_SPIN_LOCK_UNLOCKED { { 0 } }

typedef struct {
unsigned int lock;
--
1.7.5.4


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