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Keith Whitwell wrote:
> To clarify, a naive (unoptimized) usage pattern would be:
>
> LOCK_HARDWARE()
> bboffset = ValidateBuffer( i915->backbuffer )
> vboffset = ValidateBuffer( i915->vertex_buffer )
> tex0offset = ValidateBuffer( i915->tex_buffer[0] )
>
> if (!bboffset || !vboffset || !texoffset)
> FALLBACK_PATH()
> else {
> emit_state_packets();
> emit_3d_prim();
> SetFence()
> }
> UNLOCK_HARDWARE()
There is a problem with this design. You really need to validate a set
of buffers rather than one buffer at a time. Imagine the case where
those 3 buffers will exactly fill all of memory. Placing the first
buffer incorrectly will make it impossible to place the other buffers
without invalidating the first.
Other than that, this is pretty similar to what anholt, keithp, and I
came up with a few weeks ago. I just haven't started banging away at it
yet. I found it very easy to be distracted from coding projects over
the holiday. :) I believe that we used the name "CommiteBuffers"
instead of "ValidateBuffer", but the idea is the same.
I've also come around to just putting everything in the kernel. I've
been convinced (finally) that the perceived benefits of having the
actual allocator in user mode (avoiding some trips into the kernel,
having the allocation policy in user mode) don't outweigh the problems
that it creates.
> In the event of defragmentation of the address space, buffers
> validated previously within a Locked region may become invalid and
> validation of buffers will have to restart. I'll gloss over that for
> now.
I'm not 100% sure what you mean by this. Are you saying that you'd have
to loop on the ValidateBuffer calls until some steady state is achieved?
In the worst case, that loop would never terminate. :(
If you know at CommitBuffers which buffers are needed, you can try to
trivially commit the buffers (i.e., don't shuffle buffers or kick
anything out). If that fails, you shuffle buffers and kick buffers out
of memory until there is a free block large enough to hold all of the
required buffers. Then repeat the trivial commit (it *must* succeed at
this point).
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