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    Subject[PATCH 12/12] x86/ticketlock: make __ticket_spin_trylock common
    Date
    From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

    Make trylock code common regardless of ticket size.

    (Also, rename arch_spinlock.slock to head_tail.)

    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    ---
    arch/x86/include/asm/spinlock.h | 51 ++++++++-------------------------
    arch/x86/include/asm/spinlock_types.h | 6 ++-
    2 files changed, 16 insertions(+), 41 deletions(-)

    diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
    index adf010a..69f96d2 100644
    --- a/arch/x86/include/asm/spinlock.h
    +++ b/arch/x86/include/asm/spinlock.h
    @@ -70,60 +70,33 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *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");
    + arch_spinlock_t old, new;
    +
    + old.tickets = ACCESS_ONCE(lock->tickets);
    + if (old.tickets.head != old.tickets.tail)
    + return 0;

    - return tmp;
    + new.head_tail = old.head_tail + (1 << TICKET_SHIFT);
    +
    + /* cmpxchg is a full barrier, so nothing can move before it */
    + return cmpxchg_flag(&lock->head_tail, old.head_tail, new.head_tail);
    }

    +#if (NR_CPUS < 256)
    static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
    {
    asm volatile(UNLOCK_LOCK_PREFIX "incb %0"
    - : "+m" (lock->slock)
    + : "+m" (lock->head_tail)
    :
    : "memory", "cc");
    }
    #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;
    -}
    -
    static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
    {
    asm volatile(UNLOCK_LOCK_PREFIX "incw %0"
    - : "+m" (lock->slock)
    + : "+m" (lock->head_tail)
    :
    : "memory", "cc");
    }
    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;
    --
    1.7.6


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