On Wed, Mar 19, 2014 at 04:14:00PM -0400, Waiman Long wrote:
> 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.
And how does this patch do that? I think that comment is obsolete?
>
> 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@xxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> ---
> arch/x86/Kconfig | 1 +
> arch/x86/include/asm/qspinlock.h | 41 +++++++++++++++++++++++++++++++++
> arch/x86/include/asm/spinlock.h | 5 ++++
> arch/x86/include/asm/spinlock_types.h | 4 +++
> 4 files changed, 51 insertions(+), 0 deletions(-)
> create mode 100644 arch/x86/include/asm/qspinlock.h
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0af5250..de573f9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -17,6 +17,7 @@ config X86_64
> depends on 64BIT
> select X86_DEV_DMA_OPS
> select ARCH_USE_CMPXCHG_LOCKREF
> + select ARCH_USE_QUEUE_SPINLOCK
>
> ### Arch settings
> config X86
> diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
> new file mode 100644
> index 0000000..44cefee
> --- /dev/null
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -0,0 +1,41 @@
> +#ifndef _ASM_X86_QSPINLOCK_H
> +#define _ASM_X86_QSPINLOCK_H
> +
> +#include <asm-generic/qspinlock_types.h>
> +
> +#if !defined(CONFIG_X86_OOSTORE) && !defined(CONFIG_X86_PPRO_FENCE)
> +
> +#define _ARCH_SUPPORTS_ATOMIC_8_16_BITS_OPS
> +
> +/*
> + * x86-64 specific queue spinlock union structure
> + */
> +union arch_qspinlock {
> + struct qspinlock slock;
> + u8 lock; /* Lock bit */
> +};
> +
> +#define queue_spin_unlock queue_spin_unlock
> +/**
> + * queue_spin_unlock - release a queue spinlock
> + * @lock : Pointer to queue spinlock structure
> + *
> + * No special memory barrier other than a compiler one is needed for the
> + * x86 architecture. A compiler barrier is added at the end to make sure
> + * that the clearing the lock bit is done ASAP without artificial delay
> + * due to compiler optimization.
> + */
> +static inline void queue_spin_unlock(struct qspinlock *lock)
> +{
> + union arch_qspinlock *qlock = (union arch_qspinlock *)lock;
> +
> + barrier();
> + ACCESS_ONCE(qlock->lock) = 0;
> + barrier();
> +}
> +
> +#endif /* !CONFIG_X86_OOSTORE && !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 0f62f54..958d20f 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 4f1bea1..7960268 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/rwlock.h>
>
> --
> 1.7.1
>
_______________________________________________
Virtualization mailing list
Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
