Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock

[Waiman Long <waiman.long@hp.com>]

On 02/20/2014 01:42 PM, Linus Torvalds wrote:
> On Thu, Feb 20, 2014 at 9:54 AM, Waiman Long<waiman.long@hp.com>  wrote:
>> I think we could implement 2 versions of _raw_spin_lock.
> Yup. Or rather,  I'd suggest implement just one version of
> arch_spin_lock(), but at the top of it you do something like
>
>     #if CONFIG_PARAVIRT_SPINLOCK
>          if (static_key_false(&unfair_spinlocks)) {
>             .. do paravirt unfair lock version ..
>          }
>     #endif
>
> which should basically generate almost-perfect code:  it's one extra
> no-op for the native case if CONFIG_PARAVIRT_SPINLOCK is on, which
> turns into a branch for the unfair version for paravirtualization.
>
> Or something like that.
>
>                Linus

Yes, this is actually what I meant. The only difference is that I am 
thinking about using a different config variable as PARAVIRT_SPINLOCKS 
actually mean something else.

-Longman