sycl: parallelize the non-contiguous concat kernel#25852
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Launch geometry only: the non-contiguous concat kernel launched a single-lane work-group (1, 1, 1), now it will launch a (1, 1, SYCL_CONCAT_BLOCK_SIZE) one. SYCL_CONCAT_BLOCK_SIZE is defined in `ggml/src/ggml-sycl/presets.hpp`. llama-bench (Arc Pro B70, Qwen3.6-27B-UD-Q4_K_XL, -fa on, q8_0 KV), on top of upstream master: pp2048 920 -> 1006 t/s (+9.4%)
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Overview
The non-contiguous concat kernel launched a single-lane work-group (1, 1, 1), this PR changes it so that it will launch a (1, 1, SYCL_CONCAT_BLOCK_SIZE) one that can better utilize the hardware instead of having single-width iteration loops.
llama-bench (Arc Pro B70, Qwen3.6-27B-UD-Q4_K_XL, -fa on, q8_0 KV), on top of upstream master: pp2048 920 -> 1006 t/s (+9.4%)
Additional information
Should the 256 value that is shared among a bunch of macros in ggml/src/ggml-sycl/presets.hpp be dynamically set similar to #25205? I am wondering what the performance impact of setting that to 128 on Intel Alchemist hardware would be? May be faster due to 128 being the native work-group size.
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