[Xen-devel] Re: [PATCH 06/20] x86/ticketlock: make __ticket_spin_trylock common

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 11/13/2010 02:48 AM, Eric Dumazet wrote:
> Le samedi 13 novembre 2010 Ã 18:17 +0800, AmÃrico Wang a Ãcrit :
>> On Wed, Nov 03, 2010 at 10:59:47AM -0400, Jeremy Fitzhardinge wrote:
>>
>>> +   union {
>>> +           struct __raw_tickets tickets;
>>> +           __ticketpair_t slock;
>>> +   } tmp, new;
>>> +   int ret;
>>> +
>>> +   tmp.tickets = ACCESS_ONCE(lock->tickets);
>>> +   if (tmp.tickets.head != tmp.tickets.tail)
>>> +           return 0;
>>> +
>>> +   new.slock = tmp.slock + (1 << TICKET_SHIFT);
>>> +
>>> +   ret = cmpxchg(&lock->ticketpair, tmp.slock, new.slock) == tmp.slock;
>>> +   barrier();              /* just make nothing creeps before lock is 
>>> claimed */
>> This one should be smp_wmb(), right? No CONFIG_X86_OOSTORE protected.
> cmpxchg() is a full memory barrier, no need for smp_wmb() or barrier()

Agreed.

    J

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