Retrofitting quality of service into a time-sharing operating system

Theoretical aspects of proportional share schedulers have received considerable attention recently. We contribute practical considerations on how to retrofit such schedulers into mainstream time-sharing systems. In particular, we propose /reserv, a uniform API for hierarchical proportional resource sharing. The central idea in /reserv is associating resource reservations with references to shared objects (and not with the objects themselves). We discuss in detail the implementation of /reserv and several proportional share schedulers on FreeBSD; the modified system is called Eclipse/BSD. Our experiments demonstrate that the proposed modifications allow selected applications to isolate their (or their clients') performance from CPU, disk, or network overloads caused by other applications; This capability is increasingly important for soft real-time, multimedia, Web, and distributed client-server applications.