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Date: Thu, 20 Feb 2014 10:42:38 -0800
Message-ID: <CA+55aFyJTOwnSJxc_qeHxKGoZ71xo3UWc4DrAJ5=OAtOvG7_CA@mail.gmail.com>
Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
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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
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