Linux kernel cgroup v2 CFS - cpu throttled_usec accounting?

Question

In Linux kernel cgroup v2’s CFS scheduler, how is cpu.stat throttled_usec accounted when a cgroup with multiple threads gets throttled during a single quota period? Specifically, is throttled_usec tracked as the total wall-clock time that the cgroup was throttled as a whole, or is it a sum of the throttled times of all individual threads?

Kernel Version: "5.14.0-284.11.1.el9_2.x86_64 #1 SMP PREEMPT_DYNAMIC Tue May 9 11:41:53 PDT 2023 x86_64 x86_64 x86_64 GNU/Linux" Distro: Oracle Linux 9.x

I cannot understand in real time by monitoring cpu.stat file