On 26.07.2017 08:29, Michel Dänzer wrote:
On 25/07/17 05:28 PM, Nicolai Hähnle wrote:
On 22.07.2017 14:00, Daniel Stone wrote:
I don't have any great solution off the top of my head, but I'd be
inclined to bundle stride in with placement. TTBOMK (from having
looked at radv), buffers shared cross-GPU also need to be allocated
from a separate externally-visible memory heap. And at the moment,
lacking placement information at allocation time (at least for EGL
allocations, via DRIImage), that happens via transparent migration at
import time I think. Placement restrictions would probably also
involve communicating base address alignment requirements.
Stride isn't really in the same category as placement and base address
alignment, though.
Placement and base address alignment requirements can apply to all
possible texture layouts, while the concept of stride is specific to
linear layouts.
Also, the starting address of shareable buffers is generally aligned to
at least the CPU page size anyway. Do we know of any cases requiring
higher alignment than that, and if so, which address space does the
requirement apply to?
Only tiling modes, as Marek mentioned. We don't do tiling shares across
different GPUs right now.
Maybe we can do it in the future with gfx9 GPUs. But then the alignment
requirements should be known on both sides based on the tiling mode
anyway -- if they even apply for non-VRAM textures.
Given that, I'm fairly inclined to punt those until we have the grand
glorious allocator, rather than trying to add it to EGL/GBM
separately. The modifiers stuff was a fairly obvious augmentation -
EGL already had no-modifier format import but no query as to which
formats it would accept, and modifiers are a logical extension of
format - but adding the other restrictions is a bigger step forward.
Perhaps a third option would be to encode the required pitch_in_bytes
alignment as part of the modifier?
So DRI3GetSupportedModifiers would return DRM_FORMAT_MOD_LINEAR_256B
when the display GPU is a Raven Ridge.
More generally, we could say that fourcc_mod_code(NONE, k) means that
the pitch_in_bytes has to be a multiple of 2**k for e.g. k <= 31. Or if
you prefer, we could have a stride requirement in elements or pixels
instead of bytes.
Interesting idea. FWIW, I suspect we'd need to support specifying the
requirement in both bytes or pixels, since one or the other alone may
not be sufficient to describe the constraints of all hardware.
From what I've seen, modifiers are always specified together with one
specific format, so the bytes-per-pixel are always known, so I don't
think we need both. Specifying it in bytes is a bit more natural for our
hardware, that's all.
Cheers,
Nicolai
--
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.
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