Jesse Barnes <[EMAIL PROTECTED]> writes: > On Friday, June 1, 2007 2:19:43 Andi Kleen wrote: >> And normally the MTRRs win, don't they (if I remember the table correctly) >> So if the MTRR says UC and PAT disagrees it might not actually help > > I just checked, yes the MTRRs win for UC types. But it sounds like the cases > we're talking about are actually situations where there's no MTRR coverage, > so the default type is used. The manual doesn't specifically call out how > memory using the default type interacts with PAT, but it may well be that it > stays uncached if the default type is uncached. Again that argues for fixing > the MTRR mapping problem in some way.
Last I looked PAT can only demote not promote the type of a page, except for the specific exception of UC to WC. Normally the default type is UC so putting a pat type of WB won't help anything. I may have missed some subtle detail but I remember looking into this in some detail a while ago and coming to that conclusion. It is the BIOS's responsibility to mark all usable memory as WB, using the MTRRs. If it doesn't it is a BIOS bug. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
