Message-ID: <530655A3.4050105@hp.com>
Date: Thu, 20 Feb 2014 14:21:07 -0500
From: Waiman Long <waiman.long@hp.com>
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To: Linus Torvalds <torvalds@linux-foundation.org>
CC: Peter Zijlstra <peterz@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
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Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock
References: <1392669684-4807-1-git-send-email-Waiman.Long@hp.com> <53029167.4060109@zytor.com> <20140218073111.GW27965@twins.programming.kicks-ass.net> <5303B4C4.2040907@hp.com> <20140218212827.GR14089@laptop.programming.kicks-ass.net> <5303FDEC.9060001@hp.com> <20140219085107.GG27965@twins.programming.kicks-ass.net> <53050501.3070101@hp.com> <CA+55aFwyVgLJq2OgKZBK7g+T5-_M4o+dnEAr+qtYxA5t_=HSvA@mail.gmail.com> <5306413F.3010106@hp.com> <CA+55aFyJTOwnSJxc_qeHxKGoZ71xo3UWc4DrAJ5=OAtOvG7_CA@mail.gmail.com>
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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@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
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