Function read_irq_ticks 

pub(crate) fn read_irq_ticks(nr_cpus: usize) -> Option<Vec<Option<u64>>>

Per-CPU time spent in interrupt handlers, in kernel ticks, from /proc/stat (irq + softirq columns, CONFIG_IRQ_TIME_ACCOUNTING). Handler TIME is the harm itself: a wake suffers when it lands on a running handler, so line counts mis-price it; softirq is included because NAPI shadows wakes.