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fix nvcc spawning too many threads #2090

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merged 1 commit into from
Oct 22, 2025
Merged

fix nvcc spawning too many threads #2090

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31 changes: 30 additions & 1 deletion setup.py
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Original file line number Diff line number Diff line change
Expand Up @@ -496,6 +496,35 @@ def _env_enabled_any(names, default="1") -> bool:
cpp_ext = None

if cpp_ext is not None:
# Limit compile parallelism to avoid overwhelming nvcc/cicc invocations.
# Respect pre-set MAX_JOBS, otherwise fall back to CPU count minus two (min 1).
cpu_count = os.cpu_count() or 1
default_max_jobs = max(1, cpu_count - 2)
max_jobs_raw = os.environ.get("MAX_JOBS")
if max_jobs_raw is None or max_jobs_raw.strip() == "":
effective_max_jobs = default_max_jobs
print(f"MAX_JOBS not set; defaulting to {effective_max_jobs} concurrent CUDA compilations.")
else:
try:
parsed_jobs = int(max_jobs_raw)
except ValueError:
effective_max_jobs = default_max_jobs
print(f"Ignoring invalid MAX_JOBS={max_jobs_raw!r}; using {effective_max_jobs}.")
else:
if parsed_jobs <= 0:
effective_max_jobs = default_max_jobs
print(f"MAX_JOBS={parsed_jobs} is non-positive; using {effective_max_jobs}.")
else:
effective_max_jobs = parsed_jobs

os.environ["MAX_JOBS"] = str(effective_max_jobs)
os.environ["NINJA_NUM_JOBS"] = str(effective_max_jobs)
print(f"Using MAX_JOBS={effective_max_jobs} to cap concurrent CUDA compilations.")

nvcc_threads = 1
os.environ["NVCC_THREADS"] = str(nvcc_threads)
print(f"Using NVCC_THREADS={nvcc_threads} for per-invocation NVCC concurrency.")

# Optional conda CUDA runtime headers
#conda_cuda_include_dir = os.path.join(get_python_lib(), "nvidia/cuda_runtime/include")
# if os.path.isdir(conda_cuda_include_dir):
Expand Down Expand Up @@ -543,7 +572,7 @@ def _env_enabled_any(names, default="1") -> bool:
# if _version_geq(NVCC_VERSION, 13, 0):
# extra_compile_args["nvcc"].append("--device-entity-has-hidden-visibility=false")
nvcc_extra_flags = [
"--threads", "8", # NVCC parallelism
"--threads", str(nvcc_threads), # NVCC parallelism
"--optimize=3", # alias for -O3
# "-rdc=true", # enable relocatable device code, required for future cuda > 13.x <-- TODO FIX ME broken loading
# "-dlto", # compile and link <-- TODO FIX ME
Expand Down
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