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    SubjectRe: [PATCH 03/20] x86/ticketlock: Use C for __ticket_spin_unlock
    On 11/03/2010 11:13 AM, Eric Dumazet wrote:
    > Le mercredi 03 novembre 2010 à 10:59 -0400, Jeremy Fitzhardinge a
    > écrit :
    >> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    >>
    >> If we don't need to use a locked inc for unlock, then implement it in C.
    >>
    >> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    >> ---
    >> arch/x86/include/asm/spinlock.h | 33 ++++++++++++++++++---------------
    >> 1 files changed, 18 insertions(+), 15 deletions(-)
    >>
    >> diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
    >> index 6711d36..082990a 100644
    >> --- a/arch/x86/include/asm/spinlock.h
    >> +++ b/arch/x86/include/asm/spinlock.h
    >> @@ -33,9 +33,23 @@
    >> * On PPro SMP or if we are using OOSTORE, we use a locked operation to unlock
    >> * (PPro errata 66, 92)
    >> */
    >> -# define UNLOCK_LOCK_PREFIX LOCK_PREFIX
    >> +static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
    >> +{
    >> + if (sizeof(lock->tickets.head) == sizeof(u8))
    >> + asm (LOCK_PREFIX "incb %0"
    >> + : "+m" (lock->tickets.head) : : "memory");
    >> + else
    >> + asm (LOCK_PREFIX "incw %0"
    >> + : "+m" (lock->tickets.head) : : "memory");
    >> +
    >> +}
    >> #else
    >> -# define UNLOCK_LOCK_PREFIX
    >> +static __always_inline void __ticket_unlock_release(struct arch_spinlock *lock)
    >> +{
    >> + barrier();
    > technically speaking, it should be : smp_wmb()

    Perhaps. In practise it won't make a difference because it is defined
    as barrier() unless OOSTORE is defined, in which case we need to do a
    locked increment anyway.

    Thanks,
    J
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