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[Xen-devel] [PATCH RFC 06/12] x86/ticketlock: make __ticket_spin_trylock

To: Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
Subject: [Xen-devel] [PATCH RFC 06/12] x86/ticketlock: make __ticket_spin_trylock common
From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
Date: Tue, 13 Jul 2010 15:14:26 -0700
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Nick Piggin <nickpiggin@xxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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Make trylock code common regardless of ticket size.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
---
 arch/x86/include/asm/spinlock.h       |   55 +++++++++-----------------------
 arch/x86/include/asm/spinlock_types.h |    3 ++
 2 files changed, 19 insertions(+), 39 deletions(-)

diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 4f9fa24..507f83c 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -100,48 +100,25 @@ static __always_inline void __ticket_spin_lock(struct 
arch_spinlock *lock)
        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;
+       union {
+               struct __raw_tickets tickets;
+               __ticketpair_t slock;
+       } tmp, new;
+       int ret;
+
+       tmp.tickets = ACCESS_ONCE(lock->tickets);
+       if (tmp.tickets.head != tmp.tickets.tail)
+               return 0;
+
+       new.slock = tmp.slock + (1 << TICKET_SHIFT);
+
+       ret = cmpxchg(&lock->ticketpair, tmp.slock, new.slock) == tmp.slock;
+       barrier();              /* just make nothing creeps before lock is 
claimed */
+
+       return ret;
 }
-#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 4582640..48dafc3 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)
@@ -19,6 +21,7 @@ typedef u16 __ticket_t;
 typedef struct arch_spinlock {
        union {
                unsigned int slock;
+               __ticketpair_t ticketpair;
                struct __raw_tickets {
                        __ticket_t head, tail;
                } tickets;
-- 
1.7.1.1



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