Constant-Bandwidth Supply for Priority Processing – Int. Conf. on Consumer Electronics 2011 – Martijn van den Heuvel, Mike Holenderski, Reinder J. Bril and Johan J. Lukkien Systems Architecture and Networking (SAN) Department of Mathematics and Computer Science Eindhoven University of Technology The Netherlands 11 January 2011 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 1 / 22
Outline Media Processing on Virtual Platforms 1 A RELTEQ Approach 2 Constant Bandwidth Supply 3 Conclusions 4 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 2 / 22
Resource constraints and Scalable Media Processing Today’s CE-devices are heavily loaded: Multiple, independently developed applications Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 3 / 22
Resource constraints and Scalable Media Processing Today’s CE-devices are heavily loaded: Multiple, independently developed applications Trade-off: Quality versus Resources • Reuse software modules • Cost-effective • Time-to-market (Porting to new platforms) Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 3 / 22
Virtual Platform Objectives Temporal and spatial isolation, Composition and integration of subsystems on a shared platform. Each subsystem is provided a virtual processor share: Global Scheduler local local local scheduler scheduler scheduler . . . subsystem 0 subsystem 1 subsystem n Subsystem assumptions: independent subsystems 1 periodic replenished budget 2 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 4 / 22
Problem Description and Contributions Hardware virtualization is not for free: 10x increased interrupt latencies and static resource allocation, static resource allocation leads to under-utilization, not (yet) suitable for CE: data-dependent, highly fluctuating load. Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 5 / 22
Problem Description and Contributions Hardware virtualization is not for free: 10x increased interrupt latencies and static resource allocation, static resource allocation leads to under-utilization, not (yet) suitable for CE: data-dependent, highly fluctuating load. We provide software-based support for: light-weight temporal isolation, virtual timers within an application, resource reclaiming. Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 5 / 22
Mapping Priority Processing on a Virtual Platform Global Scheduler local local local scheduler scheduler scheduler . . . subsystem 0 subsystem 1 subsystem n Decision Scheduler Quality Quality 100% 100% Basic Basic B A E B A E time time Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 6 / 22 Reclaim unused capacity for enhanced media processing
Greedy Video Algorithms: Priority Processing y prel. termination t i l a u Q 100% 1. Basic: simple and fast output at low quality; Basic Quality 2. Analysis: Sort video content (0%) in order of importance; 3. Enhance: Process video content Basic Analyse Enhance according to sorted order; time Termination is allowed after a basic output is available. Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 7 / 22
Priority Processing Example Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 8 / 22
Virtual Platforms and Application-level Scheduling Global Scheduler local local local scheduler scheduler scheduler . . . subsystem 0 subsystem 1 subsystem n Decision Scheduler Quality Quality 100% 100% Basic Basic B A E B A E time time Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 9 / 22 Reclaim unused capacity for enhanced media processing
Mapping Priority Processing on Virtual Platform (Cont.) Legend: 20 ms task arrival 10 ms 10 ms task deadline server execution expiration of a virtual time slot event Server replenishment period P b = 10 ms Server budget Q b = 5 . 5 ms Video frame rate P f = 20 ms time-slot ∆ t s = 1 ms (relative to the budget Q b ) Assumptions: P f is a multiple of P b 1 P f has the same phasing as P b 2 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 10 / 22
Outline Media Processing on Virtual Platforms 1 A RELTEQ Approach 2 Constant Bandwidth Supply 3 Conclusions 4 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 11 / 22
Relative Timed-Event Queues We extended a micro-kernel with 2-levels of timer management Basic RELTEQ idea: event queue 2 15 5 0 4 Decouple global and local event management: System Queue: Keep track of global events, 1 e.g. replenishment of server budgets Server Queue: Keep track of task arrivals 2 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 12 / 22
Extending RELTEQ - Step 1 Decrement heads of all server queues: system queue 56 4 5 3 10 server queue 17 21 server queue 23 5 34 3 server queue 2 21 4 server queue 134 7 1 12 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 13 / 22
Extending RELTEQ - Step 2 Introduce a Stopwatch Queue : Track the passed time since the last server switch system queue 56 4 5 3 10 active 17 21 server queue 23 5 34 3 inactive 2 21 4 server queues 134 7 1 12 Only manage timers for the active subsystem (server). Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 14 / 22
Extending RELTEQ - Step 3 On server switch: update all heads of inactive server queues system queue 56 4 5 3 10 active 17 21 server queue -2n stopwatch queue -7 23 5 34 3 inactive 2 21 4 server queues 134 7 1 12 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 15 / 22
Final Setup: Virtual timers system queue 56 4 5 3 10 active 17 21 server queue -2n stopwatch queue -7 active 27 5 101 virtual server queue 23 5 34 3 inactive server queues & 37 4 virtual server queus Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 16 / 22
Outline Media Processing on Virtual Platforms 1 A RELTEQ Approach 2 Constant Bandwidth Supply 3 Conclusions 4 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 17 / 22
Constant Bandwidth Servers Immediately provide new budget when a budget depletes. Postpone deadline (i.e. relative priority of a server). Virtual Platform Overhead 10 µ C/OS-II with CBS µ C/OS-II 9 Overhead (% processor time) 8 7 6 5 4 3 2 1 0 1 2 3 4 5 Number of other applications in the system Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 18 / 22
Constant Bandwidth Servers and Resource Reclaiming Immediately provide new budget when a budget depletes. Postpone deadline (i.e. relative priority of a server). First use unused budget of lower priority servers. Distribution of an SVA’s progress for additional resource availability 10 ms 0.2 Frequency (number of frames) 0.1 0 20 ms 0.2 0.1 0 30 ms 0.2 0.1 0 0 10 20 30 40 50 60 70 80 Relative progress (% processed blocks) Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 19 / 22
Outline Media Processing on Virtual Platforms 1 A RELTEQ Approach 2 Constant Bandwidth Supply 3 Conclusions 4 Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 20 / 22
Conclusions Light-weight virtualization with three-level scheduling Generalized virtual timer concept, providing mechanisms for: budget enforcement 1 intra-subsystem budget management 2 Decoupled global and local event management Minimize overhead of inactive servers’ events Dynamic resource-reclaiming mechanism Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 21 / 22
References L. Abeni and G. Buttazzo. Integrating multimedia applications in hard real-time systems. In RTSS , Dec. 1998. C. Hentschel and S. Schiemenz. Priority-processing for optimized real-time performance with limited processing resources. In ICCE , Jan. 2008. M. Holenderski, W. Cools, R. J. Bril, and J. J. Lukkien. Multiplexing real-time timed events. In ETFA , July 2009. M. M. H. P. van den Heuvel, R. J. Bril, S. Schiemenz, and C. Hentschel. Dynamic resource allocation for real-time priority processing applications. Trans. on Consumer Electronics , 56(2), May 2010. Martijn van den Heuvel (TU/e, SAN) Constant-Bandwidth Supply for Priority Processing 11 January 2011 22 / 22
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