Re: [RFC Patch] use MTRR for write combining if PAT is not available

[Eric Anholt <eric@anholt.net>]

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On Thu, 2009-10-22 at 02:53 -0700, Suresh Siddha wrote:
> On Wed, 2009-10-21 at 13:01 -0700, Thomas Schlichter wrote:
> > OK, so I think the attached patches should do it. Hopefully I have addressed 
> > all your comments.
> 
> Thomas,
> 
> I have couple of issues with this patchset still. pci_mmap_page_range()
> doesn't get called for each fork(). So, we won't be ref counting the
> mtrr usage properly.
> 
> I need to think a bit more carefully on this. Can I get back to you
> early next week on this, as I am traveling and need to think through
> this?
> 
> We already keep track of some of the PAT ref counting using
> track_pfn_vma_copy(). And we need to extend/use something similar here.
> 
> Even if we need to extend sysfs or pci vma ops, we need to increment and
> decrement the ref count of the mtrr register that gets used. There is no
> need to go through num_var_ranges etc.

Can we just not create the _wc sysfs entry if we don't have PAT?  I
don't think there's userland relying on its presence as opposed to the
non-_wc entry.

-- 
Eric Anholt
eric@anholt.net                         eric.anholt@intel.com



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