Quality of Service Scheduling in Real-Time Systems

In this paper, we deal with dynamic scheduling components integrating new Quality of Service (QoS) functionalities into a Linux-based real-time operating system. In our approach, periodic tasks allow occasional deadline violations within given bounds specified according to the Skip-Over task model. Hence, every task has a minimal QoS guarantee which is expressed by the ratio of periodic task instances which must complete before their deadline. The work stated here provides two on-line scheduling algorithms, namely RLP and RLP/T, which enhance the existing Skip-Over algorithms. More specifically, the proposed algorithms aim at improving the actual QoS observed for periodic tasks (which is always greater or equal to the QoS guarantee). These novel scheduling techniques rely on the EDL (Earliest Deadline as Late as possible) scheduling strategy. Simulation results show the performance of RLP and RLP/T with respect to basic Skip-Over algorithms. Finally, we present the integration of these QoS scheduling services into CLEOPATRE open-source component library, a patch to Linux/RTAI.

[1]  Christian Poellabauer,et al.  Analysis of a window-constrained scheduler for real-time and best-effort packet streams , 2000, Proceedings 21st IEEE Real-Time Systems Symposium.

[2]  Jun Liu,et al.  A Linear-Time Optimal Acceptance Test for Scheduling of Hard Real-Time Tasks , 1994 .

[3]  Maryline Chetto,et al.  An optimal algorithm for guaranteeing sporadic tasks in hard real-time systems , 1990, Proceedings of the Second IEEE Symposium on Parallel and Distributed Processing 1990.

[4]  Giorgio C. Buttazzo,et al.  Minimizing Aperiodic Response Times in a Firm Real-Time Environment , 1999, IEEE Trans. Software Eng..

[5]  Christian Poellabauer,et al.  Dynamic window-constrained scheduling of real-time streams in media servers , 2004, IEEE Transactions on Computers.

[6]  Maryline Chetto,et al.  Some Results of the Earliest Deadline Scheduling Algorithm , 1989, IEEE Transactions on Software Engineering.

[7]  Yuting Zhang,et al.  A virtual deadline scheduler for window-constrained service guarantees , 2004, 25th IEEE International Real-Time Systems Symposium.

[8]  Alan Burns,et al.  Combining (/sub m//sup n/)-hard deadlines and dual priority scheduling , 1997, Proceedings Real-Time Systems Symposium.

[9]  Alan Burns,et al.  Weakly Hard Real-Time Systems , 2001, IEEE Trans. Computers.

[10]  Maryline Chetto,et al.  Dynamic Real-time Scheduling of Firm Periodic Tasks with Hard and Soft Aperiodic Tasks , 2006, Real-Time Systems.

[11]  Maryline Silly,et al.  The EDL Server for Scheduling Periodic and Soft Aperiodic Tasks with Resource Constraints , 1999 .

[12]  Giorgio C. Buttazzo,et al.  Exploiting skips in periodic tasks for enhancing aperiodic responsiveness , 1997, Proceedings Real-Time Systems Symposium.

[13]  Dennis Shasha,et al.  Skip-Over: algorithms and complexity for overloaded systems that allow skips , 1995, Proceedings 16th IEEE Real-Time Systems Symposium.

[14]  Parameswaran Ramanathan,et al.  A Dynamic Priority Assignement Technique for Streams with (m, k)-Firm Deadlines , 1995, IEEE Trans. Computers.

[15]  Maryline Chetto,et al.  RLP: enhanced QoS support for real-time applications , 2005, 11th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA'05).

[16]  Maryline Chetto,et al.  The EDL Server for Scheduling Periodic and Soft Aperiodic Tasks with Resource Constraints , 2004, Real-Time Systems.

[17]  Maryline Chetto,et al.  QoS scheduling components based on firm real-time requirements , 2005, The 3rd ACS/IEEE International Conference onComputer Systems and Applications, 2005..