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    Subject[PATCH v13 02/11] qspinlock, x86: Enable x86-64 to use queue spinlock
    Date
    This patch makes the necessary changes at the x86 architecture
    specific layer to enable the use of queue spinlock for x86-64. As
    x86-32 machines are typically not multi-socket. The benefit of queue
    spinlock may not be apparent. So queue spinlock is not enabled.

    Currently, there is some incompatibilities between the para-virtualized
    spinlock code (which hard-codes the use of ticket spinlock) and the
    queue spinlock. Therefore, the use of queue spinlock is disabled when
    the para-virtualized spinlock is enabled.

    The arch/x86/include/asm/qspinlock.h header file includes some x86
    specific optimization which will make the queue spinlock code perform
    better than the generic implementation.

    Signed-off-by: Waiman Long <Waiman.Long@hp.com>
    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    ---
    arch/x86/Kconfig | 1 +
    arch/x86/include/asm/qspinlock.h | 25 +++++++++++++++++++++++++
    arch/x86/include/asm/spinlock.h | 5 +++++
    arch/x86/include/asm/spinlock_types.h | 4 ++++
    4 files changed, 35 insertions(+), 0 deletions(-)
    create mode 100644 arch/x86/include/asm/qspinlock.h

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index f2327e8..9ee8324 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -122,6 +122,7 @@ config X86
    select MODULES_USE_ELF_RELA if X86_64
    select CLONE_BACKWARDS if X86_32
    select ARCH_USE_BUILTIN_BSWAP
    + select ARCH_USE_QUEUE_SPINLOCK
    select ARCH_USE_QUEUE_RWLOCK
    select OLD_SIGSUSPEND3 if X86_32 || IA32_EMULATION
    select OLD_SIGACTION if X86_32
    diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
    new file mode 100644
    index 0000000..a6a8762
    --- /dev/null
    +++ b/arch/x86/include/asm/qspinlock.h
    @@ -0,0 +1,25 @@
    +#ifndef _ASM_X86_QSPINLOCK_H
    +#define _ASM_X86_QSPINLOCK_H
    +
    +#include <asm-generic/qspinlock_types.h>
    +
    +#ifndef CONFIG_X86_PPRO_FENCE
    +
    +#define queue_spin_unlock queue_spin_unlock
    +/**
    + * queue_spin_unlock - release a queue spinlock
    + * @lock : Pointer to queue spinlock structure
    + *
    + * An effective smp_store_release() on the least-significant byte.
    + */
    +static inline void queue_spin_unlock(struct qspinlock *lock)
    +{
    + barrier();
    + ACCESS_ONCE(*(u8 *)lock) = 0;
    +}
    +
    +#endif /* !CONFIG_X86_PPRO_FENCE */
    +
    +#include <asm-generic/qspinlock.h>
    +
    +#endif /* _ASM_X86_QSPINLOCK_H */
    diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
    index 9295016..5899483 100644
    --- a/arch/x86/include/asm/spinlock.h
    +++ b/arch/x86/include/asm/spinlock.h
    @@ -42,6 +42,10 @@
    extern struct static_key paravirt_ticketlocks_enabled;
    static __always_inline bool static_key_false(struct static_key *key);

    +#ifdef CONFIG_QUEUE_SPINLOCK
    +#include <asm/qspinlock.h>
    +#else
    +
    #ifdef CONFIG_PARAVIRT_SPINLOCKS

    static inline void __ticket_enter_slowpath(arch_spinlock_t *lock)
    @@ -180,6 +184,7 @@ static __always_inline void arch_spin_lock_flags(arch_spinlock_t *lock,
    {
    arch_spin_lock(lock);
    }
    +#endif /* CONFIG_QUEUE_SPINLOCK */

    static inline void arch_spin_unlock_wait(arch_spinlock_t *lock)
    {
    diff --git a/arch/x86/include/asm/spinlock_types.h b/arch/x86/include/asm/spinlock_types.h
    index 5f9d757..5d654a1 100644
    --- a/arch/x86/include/asm/spinlock_types.h
    +++ b/arch/x86/include/asm/spinlock_types.h
    @@ -23,6 +23,9 @@ typedef u32 __ticketpair_t;

    #define TICKET_SHIFT (sizeof(__ticket_t) * 8)

    +#ifdef CONFIG_QUEUE_SPINLOCK
    +#include <asm-generic/qspinlock_types.h>
    +#else
    typedef struct arch_spinlock {
    union {
    __ticketpair_t head_tail;
    @@ -33,6 +36,7 @@ typedef struct arch_spinlock {
    } arch_spinlock_t;

    #define __ARCH_SPIN_LOCK_UNLOCKED { { 0 } }
    +#endif /* CONFIG_QUEUE_SPINLOCK */

    #include <asm-generic/qrwlock_types.h>

    --
    1.7.1


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