Scheduling Real-Time tasks on Symmetric Multiprocessor Platforms Real-Time Systems Laboratory RETIS Lab Marko Bertogna Research Area: Multiprocessor Systems

Moore’s law effects Pentium P1 P2 P4 Pentium Tejas cancelled! P3 Hot-plate Nuclear Reactor STOP Clock speed limited to less than 4 GHz Leakage current 90nm Year Power density (W/cm 2 )

Motivations Improve computing performances at reasonable power consumption. Multiprocessor-based architectures: –High-level computing: Intel’s Pentium D, Core 2 Duo, Itanium and Xeon; AMD’s Opteron, Quad FX and Athlon64 X2; etc. –Embedded market: TI’s OMAP, NXP’s Nexperia, STM’s Nomadik, ARM’s MPCore, Sony-IBM- Toshiba’s Cell, and many others. How to program these devices?

Problems Extend OS capabilities to exploit parallel computation. Adapt classical RT scheduling analysis to multi- core platforms. Develop Real-Time Multi-Processor Operating Systems (MPRTOS). Provide efficient tests to check schedulability of Multiprocessor systems. Explore “global” scheduling solutions.

Global scheduling on SMP Single system-wide queue: Preemption and Migration. Load balancing. How to sort tasks in the ready queue? Preemptive EDF is optimal only for uniprocessors. Pfair is optimal for implicit deadline systems. CPU1 CPU2 CPU3        

T Multiprocessor scheduling anomalies Scheduling problem is in general NP-hard. Schedulability problem is as well NP-hard. Dhall’s effect significantly degrades perfromances of classical scheduling algorithms. Synchronous instant is not “critical”. Only sufficient schedulability conditions. DEADLINE MISS U tot 1

Main results Sufficient schedulability tests with (pseudo-) polynomial complexity for fixed and dynamic priority multiprocessor systems. Scheduling algorithms that provide better performances on a SMP platform with bounded number of preemptions/migrations. Strategies to derive timely characteristics of given task sets, like robustness, slack, sensitivity to dynamic load variations. General analysis that can be extended for every global scheduling algorithm.

Experimental results for EDF 2 processors Constrained deadlines task sets generated Our test is constantly superior at all utilizations generated task sets our test Improvement over existing solutions Task set utilization

Experimental results for FP 2 processors Constrained deadlines task sets generated Our test is constantly superior at all utilizations generated task sets our test improvement Task set utilization

Conclusions Multiprocessor Real-Time systems are a promising field to explore. Still few existing results far from tight conditions. We contributed filling this gap. Future work: –Find tighter schedulability tests. –Use our techniques to analyze the efficiency of other scheduling algorithms (EDZL, EDF-US, FP-DS, etc). –Take into account exclusive resources access. –Integrate into Resource Reservation framework.

Marko Bertogna PhD student Real-Time Systems Laboratory RETIS Lab Thank you