On Sat, 2008-10-18 at 22:37 +0200, Ingo Molnar wrote:

quoted text
> But i think the direction of the new GEM code is subtly wrong here,=20
> because it tries to manage memory even on 64-bit systems. IMO it should=20
> just map the _whole_ graphics aperture (non-cached) and be done with it.=20
> There's no faster method at managing pages than the CPU doing a TLB fill=20
> from pagetables.

Yeah, we're stuck thinking that we "can't" map the aperture because it's
too large, but with a 64-bit kernel, we should be able to keep it mapped
permanently.

Of course, the io_reserve_pci_resource and io_map_atomic functions could
do precisely that, as kmap_atomic does on non-HIGHMEM systems today.

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> The only real API need i see is on 32-bit: with a 1GB or 2GB graphics=20
> aperture we just cannot map that permanently, so kmap_atomic() is a=20
> necessity. We can certainly extend that to non-highmem as well.

Yes, this is where exposing an io-specific atomic mapping function will
remain necessary for some time.

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> And if i understood your=20
> workload correctly you want to do tens of thousand of map/unmap/remap=20
> events per frame generated - depending on the type of the 3D app/engine.

Yeah, data transfer from CPU to GPU is through a pwrite interface, and
we perform the transfer within the kernel using map/unmap operations on
the aperture as those are WC and hence do not require clflush.

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> Or am i missing something subtle? Why do you want the overhead of kmap=20
> on 64-bit?

We don't, but I think it would be nice to have a common API that works
across all 32-bit configurations as well as 64-bit systems.

--=20
keith.packard@intel.com