Re: [PATCH [RT] 05/14] rearrange rt_spin_lock sleep

[Steven Rostedt]

On Fri, 22 Feb 2008, Ingo Molnar wrote:

>
> * Gregory Haskins <gregory.haskins.ml@xxxxxxxxx> 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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