Recent Hardness Results for Periodic Uni-processor Scheduling

Consider a set of $n$ periodic tasks $au_1,ldots, au_n$ where $au_i$ is described by an execution time $c_i$, a (relative) deadline $d_i$ and a period $p_i$. We assume that jobs are released synchronously (i.e. at each multiple of $p_i$) and consider pre-emptive, uni-processor schedules. We show that computing the response time of a task $au_n$ in a Rate-monotonic schedule i.e. computing [ minleft{ r geq mid c_n + sum_{i=1}^{n-1} leftlceil frac{r}{p_i} ight ceil c_i leq r ight} ] is (weakly) $mathbf{NP}$-hard (where $au_n$ has the lowest priority and the deadlines are implicit, i.e. $d_i = p_i$). Furthermore we obtain that verifying EDF-schedulability, i.e. [ forall Q geq 0: sum_{i=1}^n left( leftlfloor frac{Q-d_i}{p_i} ight floor +1 ight)cdot c_i leq Q ] for constrained-deadline tasks ($d_i leq p_i$) is weakly $mathbf{coNP}$-hard