Function physical_core_count 

pub fn physical_core_count() -> usize

How many physical cores this process may run on.

Clamped by available_parallelism, which is the only figure that accounts for a cgroup CPU quota — a container pinned to 8 CPUs but throttled to two cores’ worth of runtime reports 8 in its affinity mask and 2 here, and a pool built for 8 spends the difference being throttled mid-GEMV. A host with no readable topology lands on available_parallelism outright, which is the pre-topology answer.