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    Subject[PATCH 01/20] x86/ticketlock: clean up types and accessors
    Date
    From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

    A few cleanups to the way spinlocks are defined and accessed:
    - define __ticket_t which is the size of a spinlock ticket (ie, enough
    bits to hold all the cpus)
    - Define struct arch_spinlock as a union containing plain slock and
    the head and tail tickets
    - Use head and tail to implement some of the spinlock predicates.
    - Make all ticket variables unsigned.
    - Use TICKET_SHIFT to form constants

    Most of this will be used in later patches.

    Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    ---
    arch/x86/include/asm/spinlock.h | 24 ++++++++++--------------
    arch/x86/include/asm/spinlock_types.h | 20 ++++++++++++++++++--
    2 files changed, 28 insertions(+), 16 deletions(-)

    diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
    index 3089f70..d6d5784 100644
    --- a/arch/x86/include/asm/spinlock.h
    +++ b/arch/x86/include/asm/spinlock.h
    @@ -56,11 +56,9 @@
    * much between them in performance though, especially as locks are out of line.
    */
    #if (NR_CPUS < 256)
    -#define TICKET_SHIFT 8
    -
    static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
    {
    - short inc = 0x0100;
    + unsigned short inc = 1 << TICKET_SHIFT;

    asm volatile (
    LOCK_PREFIX "xaddw %w0, %1\n"
    @@ -79,7 +77,7 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)

    static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
    {
    - int tmp, new;
    + unsigned int tmp, new;

    asm volatile("movzwl %2, %0\n\t"
    "cmpb %h0,%b0\n\t"
    @@ -104,12 +102,10 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)
    : "memory", "cc");
    }
    #else
    -#define TICKET_SHIFT 16
    -
    static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)
    {
    - int inc = 0x00010000;
    - int tmp;
    + unsigned inc = 1 << TICKET_SHIFT;
    + unsigned tmp;

    asm volatile(LOCK_PREFIX "xaddl %0, %1\n"
    "movzwl %w0, %2\n\t"
    @@ -129,8 +125,8 @@ static __always_inline void __ticket_spin_lock(arch_spinlock_t *lock)

    static __always_inline int __ticket_spin_trylock(arch_spinlock_t *lock)
    {
    - int tmp;
    - int new;
    + unsigned tmp;
    + unsigned new;

    asm volatile("movl %2,%0\n\t"
    "movl %0,%1\n\t"
    @@ -160,16 +156,16 @@ static __always_inline void __ticket_spin_unlock(arch_spinlock_t *lock)

    static inline int __ticket_spin_is_locked(arch_spinlock_t *lock)
    {
    - int tmp = ACCESS_ONCE(lock->slock);
    + struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

    - return !!(((tmp >> TICKET_SHIFT) ^ tmp) & ((1 << TICKET_SHIFT) - 1));
    + return !!(tmp.tail ^ tmp.head);
    }

    static inline int __ticket_spin_is_contended(arch_spinlock_t *lock)
    {
    - int tmp = ACCESS_ONCE(lock->slock);
    + struct __raw_tickets tmp = ACCESS_ONCE(lock->tickets);

    - return (((tmp >> TICKET_SHIFT) - tmp) & ((1 << TICKET_SHIFT) - 1)) > 1;
    + return ((tmp.tail - tmp.head) & TICKET_MASK) > 1;
    }

    #ifndef CONFIG_PARAVIRT_SPINLOCKS
    diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
    index dcb48b2..4582640 100644
    --- a/arch/x86/include/asm/spinlock_types.h
    +++ b/arch/x86/include/asm/spinlock_types.h
    @@ -5,11 +5,27 @@
    # error "please don't include this file directly"
    #endif

    +#include <linux/types.h>
    +
    +#if (CONFIG_NR_CPUS < 256)
    +typedef u8 __ticket_t;
    +#else
    +typedef u16 __ticket_t;
    +#endif
    +
    +#define TICKET_SHIFT (sizeof(__ticket_t) * 8)
    +#define TICKET_MASK ((1 << TICKET_SHIFT) - 1)
    +
    typedef struct arch_spinlock {
    - unsigned int slock;
    + union {
    + unsigned int slock;
    + struct __raw_tickets {
    + __ticket_t head, tail;
    + } tickets;
    + };
    } arch_spinlock_t;

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

    typedef struct {
    unsigned int lock;
    --
    1.7.2.3


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