Resource management of the OS network subsystem

A QoS-aware real-time operating system must schedule multiple tasks which have different timing constraints and which access various resources including the CPU, disk and network. These resources, however, are not independent of one another. For example, resources like network bandwidth and disk bandwidth are available on a single node but must be managed by their host OS on the CPU by means of interrupt handlers, device drivers, file-systems and/or protocol services. Hence, in order to obtain guaranteed completion times, an application must therefore obtain both user-mode time on the CPU along with sufficient OS-level time for the network and disk subsystems. In this paper, we investigate the co-scheduling of CPU cycles and network bandwidth. Specifically, we study the problem of obtaining pre-specified network bandwidth received by applications from the external network. Our solution endows (1) direct control over the flow of network packets into the system based on the requirements of specific applications, (2)guaranteed and enforced processing time for the received packets,(3)precise accounting of those processing times, and (4)elimination of scheduling anomalies. We describe and evaluate our system design and implementation in Linux/RK, a QoS-aware real-time version of Linux. We also compare this approach with a commercial implementation we did in TimeSys Linux.