OBJECT ADAPTER ORB CORE I/O SUBSYSTEM. struct RT_Info { wc_exec_time_; period_; importance_; dependencies_; }; 1: CONSTRUCT CALL 6: SUPPLY RUN-TIME

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1 L. Levine David University, St. Louis Washington Simplify distribution automating by Object location activation and Parameter marshaling Demultiplexing Error handling Provide foundation higher-level for ORB-endsystem.ps.gz Many applications require guarantees QoS e.g., telecom, avionics, WWW Existing middleware doesn't QoS eectively support Lack of QoS specications Lack of QoS enforcement Lack of real-time programming features Lack of performance Motivation for Real-time Middleware Architectural Considerations for Real-Time CORBA ORBs and Applications e.g., CORBA, DCOM, DCE 19 May 1998 Solutions must be integrated Vertically and horizontally Sponsors: Sprint, Siemens MED and ZT, OTI, NSF grant NCR , GDIS, DARPA contract , and Boeing Washington University, St. Louis 1 Candidate Solution: CORBA Goals of CORBA Limitations Limitations of CORBA for Real-time Systems optimizations services Washington University, St. Louis 3 Washington University, St. Louis 2

2 A high-performance, ORB real-time Telecom and focus avionics Leverages the ACE framework Runs on RTOSs, and Win32 POSIX, U. RIèMITRE ARMADA, U. Mich. Specifying QoS requirements Meeting operation deadlines scheduling Alleviating priority and inversion non-determinism Reducing latencyèjitter Specifyingèenforcing QoS requirements Focus on Operations upon Objects Rather than communication channels threadsèsynchronization or Static scheduling Non-distributed Servants publish resource, e.g., CPU, and èperiodicè deadlines requirements The ACE ORB ètaoè TAO Overview Scope: Real-time Features and Optimizations in TAO Related work QuO, BBN Washington University, St. Louis 4 Washington University, St. Louis 5 Problem: Meeting End-to-End QoS Requirements Problem: Providing QoS to CORBA Operations Design Challenges Design Challenges for demultiplexing Initial focus Solution Approach Most clients are also servants Washington University, St. Louis 7 Washington University, St. Louis 6

3 Integrate RT dispatcher into endsystem ORB Support multiple request strategies scheduling e.g., RMS, EDF, and MUF Requests ordered across priorities by OS thread dispatcher Requests ordered within based on data priorities Solution: TAO's Real-time Static Scheduling Service Solution: TAO's Real-time ORB Endsystem Solution Approach dependencies and importance Washington University, St. Louis 9 Washington University, St. Louis 8 Real-time ORB Endsystem Use-case struct RT_Info { wc_exec_time_; period_; criticality_; importance_; dependencies_; }; 1: CONSTRUCT CALL CHAINS OF RT_OPERATIONS RT Operation RT Operation RT Operation OBJECT ADAPTER ORB CORE I/O SUBSYSTEM OFF-LINE SCHEDULER TAO's Real-time Dynamic Scheduling Service DEPENDS UPON = DISPATCHED AFTER 2: POPULATE RT_INFO REPOSITORY 5: ASSIGN DYNAMIC SUBPRIORITY 6: SUPPLY URGENCY TO ORB RUN-TIME SCHEDULER ENTRY PER DISPATCH OF RT_OPERATION RT_INFO REPOSITORY 3: ASSESS SCHEDULABILITY 4: ASSIGN STATIC PRIORITY (QUEUE#), STATIC SUBPRIORITY Washington University, St. Louis 11 Washington University, St. Louis 10

4 Decoupled and consumers suppliers Transparent group communication Asynchronous communication Abstraction for distribution Abstraction for Stream-based architecture Enhanced pluggability Subscriptionèltering Source and type-based ltering Event correlations Conjunctions èa+b+cè Disjunctions èajbjcè Real-time scheduling support Priority-based dispatching Priority-based preemption Interval timeouts Server factory implements thread-per-priority Highest real-time for high-priority priority client Lowest real-time for low-priority priority clients COS Event Service Features push (event) TAO's Event Service Features EVENT CHANNEL Proxies Dispatching Module Event Correlation Event Flow Subscription & Filtering Priority Timers Proxies push (event) concurrency Deadline timeouts Washington University, St. Louis 12 Washington University, St. Louis 13 RT Event Channel Use-cases Priority Inversion Experiments C 0 C C n Servants Object Adapter ORB Core SCHEDULER RUNTIME One high-priority client 1..n low-priority clients Requests Client I/O SUBSYSTEM Server ATM Switch Ultra 2 Ultra Network management Avionics Washington University, St. Louis 15 Washington University, St. Louis 14

5 52 CORBAplus High Priority MT-ORBIX High Priority minicool High Priority CORBAplus Low Priority MT-ORBIX Low Priority minicool Low Priority TAO High Priority TAO Low Priority Synopsis of results Number of Low Priority Clients CORBAplus Low Priority CORBAplus High Priority 50 MT-ORBIX Low Priority MT-ORBIX High Priority minicool Low Priority 0 minicool High Priority TAO Low Priority TAO High Priority Number of Low Priority Clients ORB Latency and Priority Inversion Results COOL's latency is lower small è of clients for TAO's latency is lowest large è of clients for TAO avoids priority inversion i.e., high priority always has client lowest latency Washington University, St. Louis 16 Concluding Remarks Developers of distributed applications confront recurring challenges that largely application-independent are e.g., service initialization and distribution, error handling, ow scheduling, event demultiplexing, concurrency control, control, persistence, fault tolerance Successful developers resolve these challenges by applying appropriate patterns to create communication frameworks and components design ORBs are an eective way to achieve reuse of distributed software components The next generation of ORBs will provide much better support for QoS real-time Washington University, St. Louis 18 ORB Jitter Results Denition Variance from latency average Synopsis of results TAO's jitter is and most lowest consistent MT-Orbix's is highest jitter more and variable Washington University, St. Louis 17 For Further Information These slides: More detail on TAO: TAO Event Channel: TAO static scheduling: TAO dynamic scheduling: ORB Endsystem Architecture: Washington University, St. Louis 19 Latency per Two-way Request in Milliseconds Jitter in milliseconds

6 Performance Measurements: For Further Information Demultiplexing latency: SII throughput: DII throughput: Latency, scalability: IIOP: More detail on CORBA: ADAPTIVE Communication Environment èaceè: Washington University, St. Louis 20