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Don't try to use NAX at run-time if kernels aren't there #2982

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Merged
awni merged 1 commit into from
Jan 13, 2026
Merged

Don't try to use NAX at run-time if kernels aren't there #2982

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4 changes: 4 additions & 0 deletions mlx/backend/metal/device.h
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Original file line number Diff line number Diff line change
Expand Up @@ -266,6 +266,9 @@ Device& device(mlx::core::Device);
std::unique_ptr<void, std::function<void(void*)>> new_scoped_memory_pool();

inline bool is_nax_available() {
#ifdef MLX_METAL_NO_NAX

@andresy andresy Jan 13, 2026

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Wouldn't it be better to positively define MLX_METAL_NAX instead when NAX is present?

@awni awni Jan 13, 2026

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Well this is the minimum edit distance version since there is one path in the cmake that we want to turn off the NAX support for but multiple in the cmake that we want it on for.

Over time I think this makes more sense as by default we will want to build to support neural accelerators... but I'm not so attached to it.. I can rearrange it if needed.

return false;
#else
auto _check_nax = []() {
bool can_use_nax = false;
if (__builtin_available(
Expand All @@ -278,6 +281,7 @@ inline bool is_nax_available() {
};
static bool is_nax_available_ = _check_nax();
return is_nax_available_;
#endif
}

} // namespace mlx::core::metal
2 changes: 2 additions & 0 deletions mlx/backend/metal/kernels/CMakeLists.txt
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Expand Up @@ -164,6 +164,8 @@ if(NOT MLX_METAL_JIT)
build_kernel(steel/attn/kernels/steel_attention_nax
${STEEL_NAX_ATTN_HEADERS})

else()
target_compile_definitions(mlx PRIVATE MLX_METAL_NO_NAX)
endif()

endif()
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