Dynamic real-time systems require adaptive resource management to accommodate varying processing needs. This paper addresses the problem of resource management on a single resource for soft real-time systems (no hard deadline requirements) consisting of tasks that have discrete quality of service (QoS) settings that correspond to varying resource requirements and varying utility. Our approach employs a feedback architecture wherein task QoS settings are adjusted on-line in order to maintain a desired amount of resource slack. These adjustments are calculated based on incremental changes in resource slack using computationally efficient algorithms that provide nearly optimal utility with computable performance bounds. The feedback architecture provides robustness in the presence of additional resource load and imperfect task resource requirement specifications.