* Linus Torvalds <[EMAIL PROTECTED]> wrote:
> [ The *non-atomic* kmap() functions are fairly high-overhead, in that they
> want to keep track of cached mappings and remember page addresses etc.
> So those are the ones we don't want to support for non-HIGHMEM setups.
>
> But the atomic kmaps are pretty simple, and really only need some
> trivial FIXMAP support. We could easily extend it for x86-64, methinks,
> and do it for x86-32 even when we don't do HIGHMEM.
>
> Ingo? ]
agreed, and there's certainly no resistance from the x86 architecture
side to extend our mapping APIs in such directions.
But i think the direction of the new GEM code is subtly wrong here,
because it tries to manage memory even on 64-bit systems. IMO it should
just map the _whole_ graphics aperture (non-cached) and be done with it.
There's no faster method at managing pages than the CPU doing a TLB fill
from pagetables.
The only real API need i see is on 32-bit: with a 1GB or 2GB graphics
aperture we just cannot map that permanently, so kmap_atomic() is a
necessity. We can certainly extend that to non-highmem as well.
But this should be an ad-hoc transitionary thing for 32-bit, and on
64-bit we really should not be using any form of kmap.
Especially with large vertex buffers or textures, mapping a lot of pages
via kmap is not going to be trivial overhead - even if INVLPG is faster
than a full TLB flush, it's still on the order of 100-200 cycles - and
with a lot of pages that mounts up quickly. And if i understood your
workload correctly you want to do tens of thousand of map/unmap/remap
events per frame generated - depending on the type of the 3D app/engine.
Or am i missing something subtle? Why do you want the overhead of kmap
on 64-bit?
Ingo
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