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fix(dflash): auto-detect GPU arch to prevent sm_120a on consumer Blackwell #48

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fix(dflash): auto-detect GPU arch to prevent sm_120a on consumer Blackwell #48

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29 changes: 29 additions & 0 deletions dflash/CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,36 @@ endif()
# the spec_prefill demo (target_gen path uses standard quant pairs).
option(DFLASH27B_FA_ALL_QUANTS "Compile ggml-cuda fattn kernels for all KV-quant pairs" ON)
set(GGML_CUDA_FA_ALL_QUANTS ${DFLASH27B_FA_ALL_QUANTS} CACHE BOOL "" FORCE)

# Use only the ggml subtree of llama.cpp (skip libllama).

# ─── CUDA architecture auto-detection ──────────────────────────────
# CUDA 12.8+ resolves "native" on Blackwell to sm_120a (DGX Spark variant).
# Query nvidia-smi at configure time to get the exact SM and set
# CMAKE_CUDA_ARCHITECTURES explicitly so ggml-cuda compiles for the
# detected physical GPU.
if(NOT CMAKE_CUDA_ARCHITECTURES OR CMAKE_CUDA_ARCHITECTURES STREQUAL "native")
find_program(_DFLASH_NVIDIA_SMI nvidia-smi)
if(_DFLASH_NVIDIA_SMI)
execute_process(
COMMAND "${_DFLASH_NVIDIA_SMI}"
--query-gpu=compute_cap --format=csv,noheader
OUTPUT_VARIABLE _dflash_gpu_caps
ERROR_QUIET
OUTPUT_STRIP_TRAILING_WHITESPACE
RESULT_VARIABLE _dflash_smi_rc
)
if(_dflash_smi_rc EQUAL 0 AND _dflash_gpu_caps)
string(REGEX MATCH "^[0-9]+\\.[0-9]+" _dflash_cap "${_dflash_gpu_caps}")
string(REPLACE "." "" _dflash_arch "${_dflash_cap}")
if(_dflash_arch)
set(CMAKE_CUDA_ARCHITECTURES "${_dflash_arch}" CACHE STRING
"CUDA architectures (auto-detected from nvidia-smi: ${_dflash_cap})" FORCE)
message(STATUS "dflash27b: GPU compute_cap ${_dflash_cap} → CUDA_ARCHITECTURES=${_dflash_arch}")
endif()
endif()
endif()
endif()
add_subdirectory(deps/llama.cpp/ggml EXCLUDE_FROM_ALL)

# The C++ sources include <cuda_runtime.h> directly, so the toolkit headers must
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