Re: Uncool feature for TTM introduced by x86, pat: Use page flagsto track memtypes of RAM pages

[Andi Kleen]

On Thu, Feb 18, 2010 at 09:38:01AM -0800, H. Peter Anvin wrote:
> On 02/18/2010 09:27 AM, Andi Kleen wrote:
> > Jerome Glisse <glisse@xxxxxxxxxxxxxxx> writes:
> >>
> >> Can we modify the interface to support again changing from uc to wc
> >> or wc to uc ? (i can try to do a patch for that).
> > 
> > At least on Intel CPUs that support self-snoop (all modern
> > ones) that should really be very cheap.
> > 
> 
> The UC/WC transition should be particularly trivial; I don't see any
> reason it should have to go through any other procedure on *any* CPU --
> selfsnoop shouldn't even figure into it, since neither UC nor WC
> actually caches anything.  For the WC->UC direction, all we should need
> to do is to flush the write combiners; a simple wmb() will do that.

I'm not sure that is sanctioned by the SDM rules; AFAIK they don't
make any special exception for this case.

-Andi
-- 
ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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