x86: work around PAGE_KERNEL_WC not getting WC in iomap_atomic_prot_pfn.

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In the absence of PAT, PAGE_KERNEL_WC ends up mapping to a memory type that
gets UC behavior even in the presence of a WC MTRR covering the area in
question.  By swapping to PAGE_KERNEL_UC_MINUS, we can get the actual
behavior the caller wanted (WC if you can manage it, UC otherwise).

This recovers the 40% performance improvement of using WC in the DRM
to upload vertex data.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

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Eric Anholt 2009-01-23 14:14:21 -08:00 • committed by Ingo Molnar

parent e1b4d11436

commit ef5fa0ab24

1 changed files with 10 additions and 0 deletions

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arch/x86/mm/iomap_32.c

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