On Wednesday, March 23, 2005 10:24 pm, Benjamin Herrenschmidt 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). It
> appears that it also disables write combining.
Doesn't pgprot_writecombine imply non-guarded, so can't you use it instead?
Either way, you'll probably want to fix fbmem.c as well and turn off
_PAGE_GUARDED?
Maybe it's time for a more generic call to support this stuff, both for
in-kernel mappings and ones that we export to userspace.
Jesse
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