Re: [PATCH 2/4, v2] x86: enlightenment for ticket spin locks - Xen implementation

Jan Beulich
2010-06-30T14:36:12Z

>>> On 30.06.10 at 16:25, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 06/30/2010 04:03 PM, Jan Beulich wrote:
>> Afaics the unlock still involves a function call *in all cases* with
>> pvops spinlocks, whereas it's a single inline instruction without.
>>
>
> No. The unlock path can see if there are any further waiters by looking
> at the ticket in the, and only do the kick call if there are some.

Are we perhaps talking about different things? I'm referring to

static __always_inline void arch_spin_unlock(struct arch_spinlock *lock)
{
PVOP_VCALL1(pv_lock_ops.spin_unlock, lock);
}

which is an indirect call which, as I understand it, gets replaced
with a direct one at runtime. But it remains to be a call (as opposed
to being a single inc instructions without CONFIG_PARAVIRT_SPINLOCKS).

Jan