Expected latency ($\mathbb{E}[T]$)

The expected value of a latency random variable. If a cache hit takes total time $t_h$, a cache miss takes total time $t_m$, and the cache hit rate is $h$, conditioning gives $\mathbb{E}[T]=h{t}_h+(1-h)t_m$. An overhead already included in either total should not be charged again.