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SubjectRe: [PATCH 13/14] x86/ticketlock: add slowpath logic
On 11/17/2010 12:31 AM, Jan Beulich wrote:
>>>> On 16.11.10 at 22:08, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>> +static inline void __ticket_enter_slowpath(struct arch_spinlock *lock)
>> +{
>> + if (sizeof(lock->tickets.tail) == sizeof(u8))
>> + asm (LOCK_PREFIX "orb %1, %0"
>> + : "+m" (lock->tickets.tail)
>> + : "i" (TICKET_SLOWPATH_FLAG) : "memory");
>> + else
>> + asm (LOCK_PREFIX "orw %1, %0"
>> + : "+m" (lock->tickets.tail)
>> + : "i" (TICKET_SLOWPATH_FLAG) : "memory");
>> +}
> Came only now to mind: Here and elsewhere, did you try using
> %z0 to have gcc produce the opcode suffix character, rather
> than having these somewhat ugly if()-s?

Actually in this case I'm pretty sure there's already a "set bit"
function which will do the job. set_bit(), I guess, though it takes a
bit number rather than a mask...

But, yes, %z0 sounds interesting. Is it documented anywhere? I think
I've tried to use it in the past and run into gcc bugs.

Thanks,
J


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