>>> On 22.03.13 at 12:58, Zhu Yanhai <zhu.yan...@gmail.com> wrote:
> Hi all,
> In the documention it reads,
>
> (2) UNLOCK operation implication:
>
> Memory operations issued before the UNLOCK will be completed before the
> UNLOCK operation has completed.
>
> Memory operations issued after the UNLOCK may be completed before the
> UNLOCK operation has completed.
>
> However, on x86-64 __ticket_spin_unlock() merely does,
>
> static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
> {
> asm volatile(
> ALTERNATIVE(UNLOCK_LOCK_PREFIX"incb (%0);"ASM_NOP3,
> UNLOCK_LOCK_ALT_PREFIX"movw $0, (%0)",
> X86_FEATURE_UNFAIR_SPINLOCK)
> :
> : "Q" (&lock->slock)
> : "memory", "cc");
> }
>
> While both UNLOCK_LOCK_PREFIX and UNLOCK_LOCK_ALT_PREFIX are empty
> strings. So how such a function keeps the memory operations issued
> before it completed?
Please read the section "Memory Ordering in P6 and More Recent
Processor Families" in SDM Vol 3.
Jan
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