Messages in this thread | | | Date | Thu, 18 Feb 2010 09:38:01 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Uncool feature for TTM introduced by x86, pat: Use page flags to track memtypes of RAM pages |
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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.
Self-snoop is about not having to flush something that can have been cached, as is normally needed to do WB/WT/WP -> UC/WC.
-hpa
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