Adaptive real-time scheduling for legacy applications Tommaso Cucinotta, Fabio Checconi, Luca Abeni, Luigi Palopoli Many applications executed nowadays on Personal Computers are multimedia applications char- acterised by soft real-time constraints. Even if they could benefit from a specialised OS support for real-time computing, the absence of standardised solutions often hinders this possibility. We propose a mechanism to export the benefits of real-time scheduling to legacy applications, based on the combination of two techniques: 1) a real-time monitor that observes the sequence of events generated by the application to infer its activation period, 2) a feedback mechanism that adapts the scheduling parameters to ensure a timely execution of the application. Categories and Subject Descriptors: D4.1 [Operating Systems]: Process Management—Schedul- ing General Terms: Experimentation, Performance, Measurement Additional Key Words and Phrases: 1. INTRODUCTION In recent times, computers have emerged as one of the most effective means to produce, store and distribute multimedia contents. They are increasingly used for video and audio streaming, surveillance, video conferencing. Such applications are usually referred to as time-sensitive, meaning that the Quality of Service (QoS) they offer is related to their ability to execute respecting some temporal constraints. In a modern computing environment, several tasks can be executed concurrently on the same processor (or processors). Therefore a prominent role for the provi- sion of temporal guarantees is taken by the scheduling policy. Common scheduling solutions adopted in General Purpose Operating Systems (GPOSs) do not offer an acceptable performance. Neither are hard real-time scheduling algorithms [Liu and Layland 1973] commonly regarded as appropriate solutions. Indeed, these algo- rithms guarantee every single deadline by making conservative assumptions on the system workload but do not provide any kind of guarantee in overload conditions. Hard real-time guarantees are not required by multimedia applications: moderate violations of temporal constraints can be easily traded for a more efficient utilisa- tion of the system as far as they are kept under control. For these applications, a superior scheduling choice is offered by such soft real-time schedulers as the resource reservations [Rajkumar et al. 1998], which guarantee a share of the CPU time to Adaptive real-time scheduling for legacy applications Permission to make digital/hard copy of all or part of this material without fee for personal or classroom use provided that the copies are not made or distributed for profit or commercial advantage, the ACM copyright/server notice, the title of the publication, and its date appear, and notice is given that copying is by permission of the ACM, Inc. To copy otherwise, to republish, to post on servers, or to redistribute to lists requires prior specific permission and/or a fee. c  20YY ACM 0000-0000/20YY/0000-0001 $5.00 ACM Journal Name, Vol. V, No. N, Month 20YY, Pages 1–0??.