Date: Fri, 22 Feb 2008 08:43:38 -0500 (EST)
From: Steven Rostedt <rostedt@goodmis.org>
To: Ingo Molnar <mingo@elte.hu>
cc: gregory.haskins@gmail.com, Gregory Haskins <ghaskins@novell.com>,
       a.p.zijlstra@chello.nl, tglx@linutronix.de,
       linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org,
       bill.huey@gmail.com, kevin@hilman.org, cminyard@mvista.com,
       dsingleton@mvista.com, dwalker@mvista.com, npiggin@suse.de,
       dsaxena@plexity.net, ak@suse.de, gregkh@suse.de, sdietrich@novell.com,
       pmorreale@novell.com, mkohari@novell.com
Subject: Re: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep
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On Fri, 22 Feb 2008, Ingo Molnar wrote:

>
> * Gregory Haskins <gregory.haskins.ml@gmail.com> wrote:
>
> > My assumption is that the xchg() (inside update_current()) acts as an
> > effective wmb().  If xchg() does not have this property, then this
> > code is broken and patch 6/14 should also add a:
>
> xchg() is a strong implicit memory barrier, it implies smp_mb().
> (historic sidenote: it was the very first SMP primitive we had in
> Linux.)

OK, I've been proven wrong ;-)

I was just thinking of how an arch would implement it. No need for memory
barriers in just an xchg. But if Linux "implies it" then that's another
story.

Thanks,

-- Steve

/me learns something new everyday.

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