Messages in this thread | | | Date | Thu, 18 Feb 2010 21:27:54 +0100 | From | Andi Kleen <> | Subject | Re: Uncool feature for TTM introduced by x86, pat: Use page flags to track memtypes of RAM pages |
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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@freedesktop.org> 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@linux.intel.com -- Speaking for myself only.
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