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Scheduling Real-Time tasks on Symmetric Multiprocessor Platforms

Scheduling Real-Time tasks on Symmetric Multiprocessor Platforms. RETIS Lab. Real-Time Systems Laboratory. Research Area: Multiprocessor Systems. Marko Bertogna. Moore’s law effects. Pentium Tejas cancelled!. Power density (W/cm 2 ). Nuclear Reactor. P4. STOP. P3. Pentium P1. P2.

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Scheduling Real-Time tasks on Symmetric Multiprocessor Platforms

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

  2. Moore’s law effects Pentium Tejas cancelled! Power density (W/cm2) Nuclear Reactor P4 STOP P3 Pentium P1 P2 Hot-plate 286 486 8086 386 8085 8080 8008 4004 Year Clock speed limited to less than 4 GHz Leakage current intolerable @ 90nm

  3. 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?

  4. 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.

  5. Global scheduling on SMP CPU1 t1 CPU2 t2 t5 t4 t3 t2 t1 CPU3 t3 • 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.

  6. Multiprocessor scheduling anomalies Utot 1 T • 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

  7. 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.

  8. Experimental results for EDF • 2 processors • Constrained deadlines • 1.000.000 task sets generated • Our test is constantly superior at all utilizations generated task sets our test Improvement over existing solutions Task set utilization

  9. Experimental results for FP • 2 processors • Constrained • deadlines • 1.000.000 • task sets • generated • Our test is • constantly • superior at all • utilizations generated task sets our test improvement Task set utilization

  10. 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.

  11. Marko BertognaPhD studentmarko@sssup.it RETIS Lab Real-Time Systems Laboratory Thank you

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