The preemptive version of the problem, along with its many variants, has been extensively studied over the years. However, little is known about the non-preemptive version of the problem, except that it is strongly NP-hard and allows a (large) constant factor approximation. Up until now, the (general) complexity of this problem is unknown. We study an important special case of the problem, where the job intervals form a laminar family, and present a quasipolynomial-time approximation scheme for it. Furthermore, we show that the special case of equal-volume jobs can be solved in polynomial-time.