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The problem of atomic addition operation failing on large-sized buffers

chen hj

When the size of Buffer<int>exceeds 65535, the atomic addition operation performed on the portion of Buffer that exceeds 65535 will not truly take effect.

I tested it using UE5's compute shader.

I tested it on MediaTek Dimensity 9300, which is G720. Is this a driver issue or a hardware limitation?

Qualcomm's Snapdragon 8Gen3 does not have this issue

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  • +1

    The driver team confirm that we do indeed have a compiler erratum that truncates the index of buffers atomics array accesses to 16-bits, which matches the fault that you are seeing. We don't know of any "neat" workaround unfortunately, so the options are really:

    • Breaking the buffer into chunks each less than 65536 entries, and indexing each chunk manually.
    • Swapping to a 2D texture buffer using a 2D index to expand the number of indexable elements.

    Kind regards, 
    Pete

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  • +1

    The driver team confirm that we do indeed have a compiler erratum that truncates the index of buffers atomics array accesses to 16-bits, which matches the fault that you are seeing. We don't know of any "neat" workaround unfortunately, so the options are really:

    • Breaking the buffer into chunks each less than 65536 entries, and indexing each chunk manually.
    • Swapping to a 2D texture buffer using a 2D index to expand the number of indexable elements.

    Kind regards, 
    Pete

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