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os.cpu_count() returns logical processors, so on SMT machines the plan sets OMP_NUM_THREADS to 2 threads/core, which thrashes the AVX-512 units during expert matmul (9950X3D: 32 logical vs 16 physical). Count RelationProcessorCore records instead, with the existing lscpu/cpu_count fallbacks intact. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>