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    Subject[PATCH 11/12] x86/ticketlock: convert __ticket_spin_lock to use xadd()
    Date
    From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

    Convert the two variants of __ticket_spin_lock() to use xadd(), which
    has the effect of making them identical, so remove the duplicate function.

    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    ---
    arch/x86/include/asm/spinlock.h | 35 +++++------------------------------
    1 files changed, 5 insertions(+), 30 deletions(-)

    diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
    index 1c8a23c..adf010a 100644
    --- a/arch/x86/include/asm/spinlock.h
    +++ b/arch/x86/include/asm/spinlock.h
    @@ -55,26 +55,22 @@
    * save some instructions and make the code more elegant. There really isn't
    * much between them in performance though, especially as locks are out of line.
    */
    -#if (NR_CPUS < 256)
    static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
    {
    - register union {
    - struct __raw_tickets tickets;
    - unsigned short slock;
    - } inc = { .slock = 1 << TICKET_SHIFT };
    + register struct __raw_tickets inc = { .tail = 1 };

    - asm volatile (LOCK_PREFIX "xaddw %w0, %1\n"
    - : "+Q" (inc), "+m" (lock->slock) : : "memory", "cc");
    + inc = xadd(&lock->tickets, inc);

    for (;;) {
    - if (inc.tickets.head == inc.tickets.tail)
    + if (inc.head == inc.tail)
    break;
    cpu_relax();
    - inc.tickets.head = ACCESS_ONCE(lock->tickets.head);
    + inc.head = ACCESS_ONCE(lock->tickets.head);
    }
    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;
    @@ -102,27 +98,6 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
    : "memory", "cc");
    }
    #else
    -static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
    -{
    - unsigned inc = 1 << TICKET_SHIFT;
    - __ticket_t tmp;
    -
    - asm volatile(LOCK_PREFIX "xaddl %0, %1\n\t"
    - : "+r" (inc), "+m" (lock->slock)
    - : : "memory", "cc");
    -
    - tmp = inc;
    - inc >>= TICKET_SHIFT;
    -
    - for (;;) {
    - if ((__ticket_t)inc == tmp)
    - break;
    - cpu_relax();
    - tmp = ACCESS_ONCE(lock->tickets.head);
    - }
    - barrier(); /* make sure nothing creeps before the lock is taken */
    -}
    -
    static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
    {
    unsigned tmp;
    --
    1.7.6


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