Stephen Tang
Email: sytang [at] cs [dot] unc [dot] edu
Office: SN324
About
I am a graduate student in the UNC-Chapel Hill Real-Time Systems Group under Professor James H. Anderson. My dissertation is on Extending Soft Real-Time Analysis for Heterogeneous Multiprocessors. I am defending in July 2024.
My research is primarily concerned with the soft real-time (i.e., deadlines can be missed as long as tardiness is bounded) properties of earliest-deadline-first (EDF) scheduling. EDF is an optimal scheduler in a soft-real-time-sense because it guarantees bounded tardiness so long as it is physically possible to do so under any scheduler. This optimality result has been proven for homogeneous multiprocessors and certain special cases of heterogeneous multiprocessors, but appears to also be true for heterogeneous multiprocessors where these proofs break down. Industry surveys have shown that many industrial applications are soft real-time. An optimal scheduler is desirable because any non-optimal scheduler will inherently introduce idle time into the schedule due to a failure to utilize all processors in the system. This increases the margin that the hardware's compute capacity must exceed the workload's utilization, which drives up cost and power requirements.
Extending soft real-time optimality results to more heterogeneous architectures is fascinating tardiness seems to remain bounded even when systems violate the assumptions used in prior proofs. Fundamentally, there is some secret ingredient to EDF that prior proofs do not take advantage of.
Teaching
I taught an undergraduate real-time systems course in Fall 2021. Feel free to email me if you'd like a copy of my lectures/assignments.Papers
Stephen Tang, Sergey Voronov, James H. Anderson. Extending EDF for Soft Real-Time Scheduling on Unrelated Multiprocessors, Proceedings of the 42nd IEEE Real-Time Systems Symposium, December 2021.
Sergey Voronov, Stephen Tang, Tanya Amert, James H. Anderson. AI Meets Real-Time: Addressing Real-World Complexities in Graph Response-Time Analysis, Proceedings of the 42nd IEEE Real-Time Systems Symposium (RTSS), December 2021.
Joshua Bakita, Shareef Ahmed, Sims H. Osborne, Stephen Tang, Jingyuan Chen, F. Don Smith, and James H. Anderson. Simultaneous Multithreading in Mixed-Criticality Real-Time Systems, Proceedings of the 27th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS), May 2021.
Stephen Tang, Luca Abeni, and James H. Anderson. On the Defectiveness of SCHED_DEADLINE w.r.t. Tardiness and Affinities, and a Partial Fix, Proceedings of the 29th International Conference on Real-Time Networks and Systems (RTNS), April 2021.
Stephen Tang and James H. Anderson. Towards Practical Multiprocessor EDF with Affinities, Proceedings of the 41st IEEE Real-Time Systems Symposium (RTSS), December 2020.
Stephen Tang, Sergey Voronov, and James H. Anderson. GEDF Tardiness: Open Problems Involving Uniform Multiprocessors and Affinity Masks Resolved, Proceedings of the 31st Euromicro Confererence on Real-Time Systems (ECRTS), July 2019.
Namhoon Kim, Stephen Tang, Nathan Otterness, James H. Anderson, F. Don Smith, and Donald E. Porter. Supporting I/O and IPC via Fine-Grained OS Isolation for Mixed-Criticality Real-Time Tasks, Proceedings of the 26th International Conference on Real-Time Networks and Systems (RTNS), October 2018.
Micaiah Chisholm, Namhoon Kim, Stephen Tang, Nathan Otterness, James H. Anderson, F. Don Smith, and Donald E. Porter. Supporting Mode Changes while Providing Hardware Isolation in Mixed-Criticality Multicore Systems, Proceedings of the 25th International Conference on Real-Time Networks and Systems (RTNS), October 2017.
Cola the cat.