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Commit ce2e2296 authored by Kenneth Graunke's avatar Kenneth Graunke Committed by Marge Bot
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iris: Suballocate BO using the Gallium pb_slab mechanism

With all the preparation in place to handle suballocated BOs at
submission and export, we can now wire up the actual suballocator.
We use Gallium's pb_slab infrastructure for this, which is already
used for this purpose in the amdgpu winsys and now zink as well.

Unlike those drivers, we don't use pb_buffer (it doesn't do much) nor
pb_cache (we already have a buffer cache).  Just pb_slab for now.

We can now suballocate BOs at power-of-two (or 3/4 power-of-two)
granularity, between 256B and 2MB.  Beyond that, we use actual GEM
objects as before.  This should save us some memory on current GPUs
where we previously had a minimum allocation granularity of 4K (page
size), but should save us a /ton/ of memory on future GPUs where the
minimum page size is 64K.  Fewer actual GEM objects should also mean
shorter exec_object2 lists passed to the kernel, which could reduce
CPU overhead a bit.  Using large allocations where the underlying
GEM objects correspond with the PTE fragment size may also allow the
kernel to use a more efficient page table layout, improving memory
access times.

This cuts nearly half of the memory usage in a Unity3D demo on a
GPU that uses 64K pages.

Closes: mesa/mesa#4722



Acked-by: default avatarPaulo Zanoni <paulo.r.zanoni@intel.com>
Part-of: <mesa/mesa!12623>
parent b8ef3271
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