On 10/16/2009 03:51 AM, Anthony Liguori wrote:
Avi Kivity wrote:
One way to improve the gfn_to_pfn() memslot search is to register
just one slot. This can only work on 64-bit, since even the smallest
guests need 4GB of physical address space. Apart from speeding up
gfn_to_page(), it would also speed up mmio which must iterate over
all slots, so a lookup cache cannot help.
This would require quite a bunch of changes:
- modify gfn_to_pfn() to fail gracefully if the page is in the slot
but unmapped (hole handling)
- modify qemu to reserve the guest physical address space
It could potentially speed up qemu quite a lot too as we would return
to a model where host va == fixed address + guest pa. That makes
things like stl_phys/ldl_phys trivial.
This doesn't work on 32-bit, and you still need to perform a lookup for
mmio. It just shortens the loop.
Note qemu can't depend on mmio holes being unmapped (you could trap the
SEGV, but that would be unbearably slow).
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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