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Slide title In CAPITALS 50 pt Slide subtitle 32 pt PowerPoint Presentation
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Slide title In CAPITALS 50 pt Slide subtitle 32 pt

Slide title In CAPITALS 50 pt Slide subtitle 32 pt

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Slide title In CAPITALS 50 pt Slide subtitle 32 pt

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  1. Slide title In CAPITALS 50 pt Slide subtitle 32 pt Status & Plans Work package 4 Tasks 4.1 and 4.3 Bandwidth Schemes and Resource Constraints

  2. Brief Description • Find a suitable bandwidth reservation algorithm • Many existing servers • Need to introduce a classification • Take into account shared resources • Tight connection to • Task 4.4: Multi-core reservation • Task 4.5: RBS on Linux • Output  Task 4.2: Requirements/QoS interface

  3. Existing Servers (!!!) CBS, GRUB, SHRUB, CASH, BASH, simplified CASH, SRAND,SLAD,SLASH,BACKSLASH, IRIS, CSS, HLS, BEBS, RBED, VRE, RED, ROBUST, RHD, Slack stealing, Capacity Sharing, HisReWri, hier sched, H-CBS, H-GPS, Offline aperiodic scheduling, Deferrable Server, Sporadic Server, Periodic or Polling Server, Priority Exchange, Deadline Deferrable Server (DDS), Deadline Sporadic Server (DSS), Deadline Exchange Server (DXS), TBS, Dynamic Priority Exchange (DPE), Dynamic Sporadic Server, EDL, Improved Priority Exchange (IPE), BSS, TB*, Processor reservation, EEVDF (Earliest Eligible Virtual Deadline First), Proportional share, WFQ, WF2Q, WF2Q+, SMART, BVT, (Start-Time Fair Queuing) SFP, Spare CASH, etc.

  4. Brief Description • Deliverables and timeline • Task 4.1 • journal submission with servers classification (expected by early ’09) • Task 4.3 • Two papers detailing shared resource protocols for single CPU and hierarchical servers (SAC and RTSS) • Integration with task 4.4: • Multiprocessor shared resource protocol (ECRTS’09) • Shared resource protocol for Hierarchical Multicore systems (RTSS’09)

  5. This is how we work together • Tight interaction between SSSA and Evidence (both in Pisa) • SSSA • Marko Bertogna, Fabio Checconi, Dario Faggioli, Antonio Mancina, Luca Santinelli • Evidence • Michael Trimarchi (currently in Valencia) • Theoretical aspects  SSSA • Implementation  ½ Evidence, ½ SSSA • Weekly discussion

  6. So far • Publications (downloadable from my homepage) • Implementing a Partitioned Earliest Deadline First Algorithm in Linux (accepted SAC’09) • Non-Preemptive Access to Shared Resources in Hierarchical Real-Time Systems (CRTS’08) • Algorithms • Shared resource protocol for hierarchical systems (single processor only) • Maximum available non-preemptive chunk length (different complexities) • Algorithms implemented in a Linux patch

  7. Budget exhaustion problem Server 1 Q = 10, P = 100 Lock (R1) Unlock (R1) Server 2 Q = 90, P = 100 BLOCKED

  8. Solution • Perform a “budget check” before each locking operation • BROE server (Fisher, Bertogna, Baruah – RTSS’07) • CBS-like server for hierarchical systems with support for globally shared resources • If CS_length ≤ q  acquire lock • Else  wait until virtual time equals real time q = 10 Lock (R1) Q = 10 P = 100 |CS| = 5 q = 4 WAIT

  9. Non-preemptive access to shared resources • Disable preemptions before each locking operations • No need for complex locking protocols • Reduced resource holding times • Very efficient with small CS lengths • Simple algorithm to derive a safe non-preemptive chunk length • Polynomial: O(1), O(n) • Pseudo-polynomial: O(Pmax)

  10. Admission control • No need to know a priori the critical section lengths • Keep track of the maximum CS length recorded • When some CS exceeds available h length  take some decision

  11. Next Step • Adapt our reservation protocol to multicore systems • Generalize to multicore hierarchical systems • Schedulability tests and/or tardiness bounds for hierarchical multiprocessor systems • Implement in Linux (particular attention to overall complexity) • Final results expected by the end of 2009

  12. Thank you Marko Bertogna - Scuola Superiore Sant’Anna, Pisa marko@sssup.it Papers downloadable from http://retis.sssup.it/~marko/