An Overview of Distributed Real-Time Systems Research
description
Transcript of An Overview of Distributed Real-Time Systems Research
![Page 1: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/1.jpg)
An Overview of Distributed Real-Time Systems Research
By Brian DemersMarch 24, 2003
CS 535, Spring 2003
![Page 2: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/2.jpg)
Project Overview• Examine efforts to combine real-
time and distributed computing ideas
• Summarize trends, focal points– Tried not to filter ideas
• Examine one or more sample implementations (if possible)
• Work in progress!
![Page 3: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/3.jpg)
Presentation Overview
• Definitions of key terms, issues• Discussion of key research areas,
developments– Networks– Scheduling
• To-do list• Conclusions, questions,
suggestions
![Page 4: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/4.jpg)
Definitions
• Hard vs. soft real-time• Distributed systems
– Did not consider traditional parallel computers
General focus: soft RT systems
![Page 5: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/5.jpg)
Networking
![Page 6: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/6.jpg)
Networking
• Inherently non-deterministic– Research focus is on LAN
configurations
• Main approaches– Improve determinism of existing
protocols– Use probabilistic approach
![Page 7: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/7.jpg)
Ethernet
• Pros– Cheap– Widely used
• Cons– Not designed for real-time use– Packet arrival times can vary widely
![Page 8: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/8.jpg)
Ethernet Improvements
• Halmsted University– Hardware solution:
Propose a network connected exclusively by switches (eliminating collisions)
– Switches perform data buffering, manage real-time streams
Switch
![Page 9: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/9.jpg)
Ethernet Improvements (cont.)• Traffic smoothing
(Kweon, Shin, and Workman)– Probabilistically limit
traffic into network
• Virtual token ring (Chiueh and Venkatramani)– Switch to token-based
scheme when RT traffic detected
Data-link Layer
Regulator
Higher NetworkLayers
Traffic smoothing approach
![Page 10: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/10.jpg)
Token-Based Protocols
• Pros– Fairly deterministic (for a network)
• Cons– Not as widely available– Latencies can be high (according to
some)
![Page 11: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/11.jpg)
Token-Based Protocols (cont.)
• FDDI (Fiber Distributed Data Interface)– Uses token-based, ring topology– Data rates equivalent to Fast Ethernet– Fault tolerant
• RTFC (RT Fiber Communications)
• Not much recent work on IEEE 802.5
![Page 12: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/12.jpg)
Scheduling
![Page 13: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/13.jpg)
Scheduling
• Packet scheduling• Task scheduling• Resource scheduling
![Page 14: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/14.jpg)
Packet Scheduling
• Vital for RT communications• Some probabilistic work • Some work with co-scheduling RT
and non-RT packets
![Page 15: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/15.jpg)
Packet Scheduling (cont.)
• Concatenated Hybrid Automatic Repeat Request (Uhlemann et al.)– Repeated transmissions– Signal averaging
• (m, k) scheduling (Hamdaoui and Ramanathan)– Some work on a distance-based priority
scheme to guarantee this– Extended to multi-hop networks
![Page 16: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/16.jpg)
Packet Scheduling (cont.)
• Combining RT traffic with non-RT traffic (Chakraborty, Gries, and Thiele)– Use Earliest Deadline First (EDF)
scheduling– Assign deadlines so that RT & NRT
traffic can coexist– Claimed 25-45% improvement for
NRT traffic
![Page 17: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/17.jpg)
Task Scheduling
• Landmark paper: Liu & Layland (1973)– Analyzed static and dynamic scheduling
(single processor)– Many efforts to extend this
• Distributed Generalized Multiframe (DGMF) model (Chen, Mok, and Baruah)– Presents new analytical framework
![Page 18: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/18.jpg)
Task Scheduling (cont.)
• Breaking tasks into subtasks (Kao and Garcia-Molina)– Setting subtask
deadlines– Methodologies,
performance issues
Task
Subtask
Subtask
Sub-task
Subtask
![Page 19: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/19.jpg)
Task Scheduling (cont.)
• Resource fragmentation (Bestavros)– Load balancing– Potentially bad for
CPU-intensive jobsCPU 1 CPU 2 CPU 3
60%50%
70%
Example:
![Page 20: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/20.jpg)
Sample Systems
![Page 21: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/21.jpg)
Sample DRT Systems
• Everyone cites the same examples– Air-traffic control, factory automation,
nuclear power plants, etc.– Difficult to find much info about these
topics!
• Some work from avionics• Possibly some air-traffic systems
(FAST?)
![Page 22: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/22.jpg)
Summary
![Page 23: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/23.jpg)
Distributed RT: Research Focus
• Networking– Extending Ethernet to RT apps– Packet scheduling issues
• Working with “soft” RT systems– Leads to probabilistic techniques
![Page 24: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/24.jpg)
To-do: Remaining Efforts
• More detail on resource usage, scheduling
• RT evaluation of token-based networks
• Find and examine sample implementation
![Page 25: An Overview of Distributed Real-Time Systems Research](https://reader035.fdocuments.in/reader035/viewer/2022062519/56814e4a550346895dbbd43a/html5/thumbnails/25.jpg)
Questions/Suggestions?