drm/i915: Convert clflushed pagetables over to WC maps
We flush the entire page every time we update a few bytes, making the update of a page table many, many times slower than is required. If we create a WC map of the page for our updates, we can avoid the clflush but incur additional cost for creating the pagetable. We amoritize that cost by reusing page vmappings, and only changing the page protection in batches. Signed-off-by:Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by:
Mika Kuoppala <mika.kuoppala@intel.com>
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