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SubjectRe: [rfc][patch 2/3] x86: fix IO write barriers
Date
On Thursday 04 October 2007 20:10:44 Dave Jones wrote:
> On Thu, Oct 04, 2007 at 07:53:16PM +0200, Andi Kleen wrote:
> >
> > > The only vendor that ever implemented OOSTOREs was Centaur, and they
> > > only did in the Winchip generation of the CPUs. When they dropped it
> > > from the C3, I asked whether they intended to bring it back, and the
> > > answer was "extremely unlikely".
> > >
> >
> > Do you know if it made a big performance difference?
>
> On the winchip, it was a huge win. I can't remember exact numbers,
> but pretty much every benchmark I threw at it at the time showed
> significant improvement.

Significant as in >10%?


> > But yes we should probably just remove this special case to make
> > maintenance easier.
>
> It's CONFIG_SMP anyway, which none of the winchips were.

It's not. And we need memory barriers even without SMP
when talking to device drivers. Only the smp_*b()s get noped
on UP.

-Andi
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