b10785

metal : add sparse FA (#28098)

• metal : support n_kv_max sparse mask hint in flash attention vec kernel

• add kernel_flash_attn_ext_vec_idx: compacts finite mask entries into
  a per-row index list (Hillis-Steele scan, one threadgroup per row)
• extend vec FA kernel with optional sparse index gathering (FC slot 5)
• add host-side gate: sparse path when n_kv_max > 0, mask present,
  supported head sizes / KV types, n_kv_max <= 4096
• new buffer region extra_idx for the index list
• pipeline getter extended with has_sparse param
• add test cases: head sizes, quant types, nb>1, nr23 variants,
  sinks, ALiBi, softcap, permute, v_view_of_k, no-mask fallback

Note: multi-row (nb*nr23[1] > 1) cases still failing - rid mapping
in the store phase needs revisiting for the sparse path.

Assisted-by: pi:llama.cpp/Qwen3.8-27B

• metal : fix sparse flash attention row addressing

• kernel_flash_attn_ext_vec_idx: mask param is half* but nb31 is a byte
  stride, so the per-row mask offset was scaled by 2x; cast to char*
  before applying the byte strides
• kernel_flash_attn_ext_vec: sparse pidx param is char* so the per-row
  element offset was under-scaled by sizeof(int); scale it by sizeof(int)
  to get the correct byte offset
• fixes the multi-row (nb*nr23[1] > 1) sparse flash attention failures

Assisted-by: pi:llama.cpp/DeepSeek-v4-0731

• cont : use sparse vec FA for prefill

• metal : single-pass flash attention sparse index compaction

The idx kernel previously read the mask row twice: once to count the finite
entries (for the prefix scan) and again to recover their positions. Since the
kernel is memory-bound, this doubled the mask traffic.

Keep the finite positions in a per-thread register array during the count
pass and write them out directly, avoiding the second mask read. A dense
mask with more than NLOCAL finite entries in a slice falls back to re-reading
the mask to write the remaining positions.

Assisted-by: pi:llama.cpp/DeepSeek-v4-0731

• tests : add perf cases for sparse flash attention prefill

Measure the sparse vec FA kernel across KV sizes, n_kv_max hints and batch
sizes. Run with:

./build/bin/test-backend-ops -b MTL0 -o FLASH_ATTN_EXT -p "n_kv_max=[1-9]" perf

Assisted-by: pi:llama.cpp/DeepSeek-v4-0731

• qwen4 : enable sparse attention

• cont : adjust nsg

• cont : sync test-backend-ops

• cont : disable Qwen4 for now

• cont : clean-up + tests

Website:

• https://llama.app

Attestations:

• https://github.com/ggml-org/llama.cpp/attestations/44984034

macOS/iOS:

• macOS Apple Silicon (arm64)
• macOS Apple Silicon (arm64, KleidiAI enabled) DISABLED
• macOS Intel (x64)
• iOS XCFramework

Linux:

• Ubuntu x64 (CPU)
• Ubuntu arm64 (CPU)
• Ubuntu s390x (CPU)
• Ubuntu x64 (Vulkan)
• Ubuntu arm64 (Vulkan)
• Ubuntu x64 (ROCm 10.0)
• Ubuntu x64 (OpenVINO)
• Ubuntu x64 (SYCL FP32)
• Ubuntu x64 (SYCL FP16)

Android:

• Android arm64 (CPU)

Windows:

• Windows x64 (CPU)
• Windows arm64 (CPU)
• Windows arm64 (OpenCL Adreno)
• Windows x64 (CUDA 12) - CUDA 12.4 DLLs
• Windows x64 (CUDA 13) - CUDA 13.3 DLLs
• Windows arm64 (CUDA 13) (preview) - CUDA 13.4 DLLs
• Windows x64 (Vulkan)
• Windows x64 (OpenVINO)
• Windows x64 (SYCL)
• Windows x64 (ROCm 10.0)

openEuler:

• DISABLED
• openEuler x86 (310p)
• openEuler x86 (910b, ACL Graph)
• openEuler aarch64 (310p)
• openEuler aarch64 (910b, ACL Graph)

UI:

• UI