Messages in this thread | | | Subject | Re: [PATCH] ppc32/64: Map prefetchable PCI without guarded bit | From | Benjamin Herrenschmidt <> | Date | Sat, 26 Mar 2005 09:26:52 +1100 |
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On Thu, 2005-03-24 at 19:20 +0100, Segher Boessenkool wrote: > > While experimenting with framebuffer access performances, we noticed a > > very significant improvement in write access to it when not setting > > the "guarded" bit on the MMU mappings. This bit basically says that > > reads and writes won't have side effects (it allows speculation). > > Unless the data is already in cache. > > > It appears that it also disables write combining. > > When the page is also cache-inhibited, it indeed does. > > > Btw, did you ever get to fix the problem with mapping the last page > of physical address space via /dev/mem ?
I don't think so, but I'll have to double check.
Ben.
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