Am 17.02.23 um 14:10 schrieb Thomas Hellström:
[SNIP]
Any chance you could do a quick performance comparison? If not,
anything against merging this without the amd / radeon changes
until we can land a simpler allocator?
Only if you can stick the allocator inside Xe and not drm, cause
this seems to be for a different use case than the allocators
inside radeon/amdgpu.
Hmm. No It's allocating in a ring-like fashion as well. Let me put
together a unit test for benchmaking. I think it would be a failure
for the community to end up with three separate suballocators doing
the exact same thing for the same problem, really.
Well exactly that's the point. Those allocators aren't the same
because they handle different problems.
The allocator in radeon is simpler because it only had to deal with a
limited number of fence timelines. The one in amdgpu is a bit more
complex because of the added complexity for more fence timelines.
We could take the one from amdgpu and use it for radeon and others as
well, but the allocator proposed here doesn't even remotely matches
the requirements.
But again, what *are* those missing requirements exactly? What is the
pathological case you see for the current code?
Well very low CPU overhead and don't do anything in a callback.
From what I can tell the amdgpu suballocator introduces excessive
complexity to coalesce waits for fences from the same contexts,
whereas the present code just frees from the fence callback if the
fence wasn't already signaled.
And this is exactly the design we had previously which we removed after
Dave stumbled over tons of problems with it.
The fence signalling code that fires that callback is typcally always
run anyway on scheduler fences.
The reason we had for not using the amdgpu suballocator as originally
planned was that this complexity made it very hard for us to undertand
it and to fix issues we had with it.
Well what are those problems? The idea is actually not that hardware to
understand.
We could simplify it massively for the cost of only waiting for the
oldest fence if that helps.
Regards,
Christian.
Regards,
Thomas
