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

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On 02/20/2014 01:42 PM, Linus Torvalds wrote:
On Thu, Feb 20, 2014 at 9:54 AM, Waiman Long<waiman.long@xxxxxx>  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
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