ryankert01 commented on code in PR #1321:
URL: https://github.com/apache/mahout/pull/1321#discussion_r3265910589
##########
qdp/qdp-core/build.rs:
##########
@@ -34,3 +42,54 @@ fn main() {
println!("cargo:rerun-if-changed=proto/tensor.proto");
}
+
+/// Detect the CUDA Runtime toolkit and emit the appropriate link directives.
+///
+/// `qdp-core` declares CUDA Runtime API extern symbols in
`src/gpu/cuda_ffi.rs`
+/// (cudaHostAlloc, cudaMemGetInfo, cudaEventCreateWithFlags, ...). Those
symbols
+/// must be resolved at link time, which requires `libcudart` from the CUDA
+/// Toolkit. Previously the only `-lcudart` directive lived in `qdp-kernels`'
+/// build script, and the `qdp_no_cuda` cfg it sets does not propagate
+/// cross-crate. The result was confusing linker errors on systems that have
+/// the NVIDIA driver but not the toolkit (e.g. PyTorch-only setups, where
+/// PyTorch ships its own bundled cudart inside the wheel).
+///
+/// This function:
+/// * emits `cargo:rustc-link-lib=cudart` and the appropriate
+/// `cargo:rustc-link-search` path when nvcc is found, and
+/// * emits `cargo:rustc-cfg=qdp_no_cuda` when it is not, gating the
Review Comment:
`output().is_ok()` is true even if nvcc exits non-zero — a half-installed
nvcc would set `has_cuda = true` and fall through to a link error. Suggest
`.map(|o| o.status.success()).unwrap_or(false)`. Same idiom in
`qdp-kernels/build.rs:177`; fix both so they can't disagree.
##########
qdp/qdp-core/build.rs:
##########
@@ -34,3 +42,54 @@ fn main() {
println!("cargo:rerun-if-changed=proto/tensor.proto");
}
+
+/// Detect the CUDA Runtime toolkit and emit the appropriate link directives.
+///
+/// `qdp-core` declares CUDA Runtime API extern symbols in
`src/gpu/cuda_ffi.rs`
+/// (cudaHostAlloc, cudaMemGetInfo, cudaEventCreateWithFlags, ...). Those
symbols
+/// must be resolved at link time, which requires `libcudart` from the CUDA
Review Comment:
Missing `cargo:rerun-if-env-changed=PATH`. The whole decision hinges on
nvcc-on-PATH, so installing CUDA after a stub build won't re-trigger the script
until `cargo clean`. Same gap in qdp-kernels.
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