  We consider the problem of energy-efficient scheduling across multiple
processors with a power-down mechanism. In this setting a set of $n$ jobs with
individual release times, deadlines, and processing volumes must be scheduled
across $m$ parallel processors while minimizing the consumed energy. Idle
processors can be turned off to save energy, while turning them on requires a
fixed amount of energy. For the special case of a single processor, the greedy
Left-to-Right algorithm guarantees an approximation factor of $2$. We
generalize this simple greedy policy to the case of $m \geq 1$ processors
running in parallel and show that the energy costs are still bounded by $2
\text{OPT} + P$, where $\text{OPT}$ is the energy consumed by an optimal
solution and $P < \text{OPT}$ is the total processing volume. Our algorithm has
a running time of $\mathcal{O}(n f \log d)$, where $d$ is the difference
between the latest deadline and the earliest release time, and $f$ is the
running time of a maximum flow calculation in a network of $\mathcal{O}(n)$
nodes.
