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ggml-org-llama-cpp-mirror/tests
François-Xavier Gsell b3daa077a5 vulkan: sparse flash attention for quantized K/V (#29639)
* vulkan: sparse flash attention for quantized K/V

Assisted-by: Claude

* vulkan: single-scan sparse FA index compaction

The compaction ran one workgroup per mask row and walked the row in
BLOCK_SIZE chunks, with a workgroup scan per chunk. For decode that is
one workgroup doing KV/1024 barrier-bound iterations, so at 128k cells
it cost more than the sparse attention it feeds.

Split the row into contiguous segments instead: one per subgroup with
ballot counting over coalesced loads, or one per thread without
subgroups. A single scan over the segment counts then gives each
segment its output offset. The index list stays ascending.
2026-10-05 10:37:54 +02:00
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