A critique of the GNU hurd multi-server operating system
ACM SIGOPS Operating Systems Review
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Abstract: An important class of adaptive applications can trade off one kind of resources (e.g., network bandwidth) for requests of other resources (e.g., CPU cycles). They create new challenges for operating systems: their processor demands change rapidly based on external factors, and resource requests are recurring, though non-periodic. However, these applications share some of the characteristics of "soft real-time" tasks and are often resilient with regard to un- or under-availability of resources. This paper presents a comprehensive approach to processor management for adaptive applications, the R-Scheduler. It co-exists with a best-effort scheduler and has been implemented for NetBSD and ported to Linux. The runtime costs of admission control and scheduling are modest (below 1%). For realistic usage scenarios, the R-Scheduler allows the application to meet its time limits, whereas the traditional (default) best-effort scheduling discipline fails to allocate the CPU resources effectively.