Why do you care about performance when PAT is disabled?
breaking old boxes just because, is just going to get reverted when I get the first regression report that you broke old boxes.
Andy Lutomirski just submitted a bunch of patches to clean up the DRM usage of mtrrs, they are in drm-next, afaik we no longer add them on PAT systems.
Dave.
It will regress already slow boxes. We blacklist a LOT of P4s, PMs, etc and nobody ever took the pain to track down which ones of those actually have PAT+MTRR aliasing bugs.
These boxes have boards like the Radeon X300, which needs either PAT or MTRR to not become unusable...
We're talking hardware which is now many years old, but this is causing very serious problems on real, modern hardware. As far as I understand it, too, the blacklisting was precautionary (the only bug that I personally know about is a performance bug, where WC would be incorrectly converted to UC.)
We need a way forward here. If it is the only way I think we would have to sacrifice the old machines, but perhaps something can be worked out (e.g. if PAT is disabled, fall back to MTRRs if available for ioremap_wc()).
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