On Wed, Dec 14, 2005 at 02:12:53AM +0100, Andi Kleen wrote:
> On Tue, Dec 13, 2005 at 02:50:59PM -0800, Paul E. McKenney wrote:
> > On Wed, Dec 14, 2005 at 09:27:41AM +1100, Keith Owens wrote:
> > > On Tue, 13 Dec 2005 08:20:27 -0800,
> > > "Paul E. McKenney" <[email protected]> wrote:
> > > >If the variable p references MMIO rather than normal memory, then
> > > >wmb() and rmb() are needed instead of smp_wmb() and smp_rmb().
> > >
> > > mmiowb(), not wmb(). IA64 has a different form of memory fence for I/O
> > > space compared to normal memory. MIPS also has a non-empty form of
> > > mmiowb().
> >
> > New one on me!
>
> Didn't it make only a difference on the Altix or something like that?
> I suppose they added it only on the drivers for devices supported by SGI.
It could potentially help on a few other CPUs, but quite a few driver
changes would be needed to really bring out the full benefits. I am
concerned that the current state leaves a number of CPU families broken --
the empty definitions cannot be good for other weakly ordered CPUs!
Thanx, Paul
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