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SubjectRe: [PATCH 13/14] x86/ticketlock: add slowpath logic
On 11/17/2010 10:52 AM, Jeremy Fitzhardinge wrote:
> 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...
>

set_bit() operates on a long, while the intel manuals recommend against
operating on operands of different size, especially with locked
operations. I think newer processors have more relaxed requirements,
though.

--
error compiling committee.c: too many arguments to function



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