Measuring OS Support for Real-time CORBA ORBs Christopher D. Gill - - PowerPoint PPT Presentation

Measuring OS Support for Real-time CORBA ORBs

Christopher D. Gill Washington University, St. Louis cdgill@cs.wustl.edu 27 January 1999 http://www.cs.wustl.edu/

Sponsors: Boeing, CDI/GDIS, DARPA contract 9701516, Lucent, Motorola, NSF grant NCR-9628218, Siemens, and Sprint

Christopher D. Gill Real-Time ORBs

Advantages of CORBA

• www.cs.wustl.edu/ schmidt/

ORB-endsystem.ps.gz

– Simplify distribution by automating

and activation

marshaling

– Provide foundation for higher-level services

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Christopher D. Gill Real-Time ORBs

Limitations of CORBA for Real-time Systems

• Limitations

– Lack of QoS specifications – Lack of QoS enforcement – Lack of real-time programming features – Lack of performance

• ptimizations

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Christopher D. Gill Real-Time ORBs

But Can It Perform?

– context switch time – request-response latency – ORB/endsystem CPU overhead

– context switch time – request-response latency

– request-response jitter

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Christopher D. Gill Real-Time ORBs

Context Switch Time Measurements

Operating Context Switch Time,

System mean (standard deviation) Suspend- Yield Test Synch Test Resume Test VxWorks 0.946 (0.041) N/A 1.62 (0.023) LynxOS N/A 5.42 (0.008) 5.96 (0.042) Windows NT 1.41 (0.036) 1.78 (0.021) 2.79 (0.110) Solaris 21.3 (0.569) 11.2 (0.900) 131.2 (0.613) Linux N/A 2.60 (0.023) 9.72 (0.187) Table 1: Context Switch Time Measurements

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Christopher D. Gill Real-Time ORBs

Context Switch Time Measurements

expected

impair performance predictability

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Christopher D. Gill Real-Time ORBs

Priority Inversion Experiments

• [P ]

C 0 C

• 1

[P ]

C

Pentium II

2

1

C 3

3

[P ]

[P ]

[P ]

S

3

3

2

[P ]

S 2

2

I/O SUBSYSTEM

Server

1

RUNTIME SCHEDULER

[P ] S S

Object Adapter Servants

Client

[P] Requests Priority

[P ]

1

ORB Core

implements thread-per-connection – Higher real-time priority for high-priority client – Lower real-time priority for all low-priority clients

client with its servant

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Christopher D. Gill Real-Time ORBs

ORB Latency and Priority Inversion Results

200 400 600 800 1000 1200 Linux LynxOS NT Solaris VxWorks Operating System Two-way Request Latency, usec

20 Hz 10 Hz 5 Hz 1 Hz

– LynxOS and Linux provide lowest latency – LynxOS and VxWorks do not exhibit priority inversion; non-RTOS’s do – Therefore, deterministic QoS support requires a RTOS

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Christopher D. Gill Real-Time ORBs

ORB Jitter Results

100 200 300 400 500 600 Linux LynxOS NT Solaris VxWorks Operating System Two-way Request Jitter, usec

20 Hz 10 Hz 5 Hz 1 Hz

– Standard deviation from average latency

– LynxOS and VxWorks show low jitter – Linux, Windows NT, and Solaris show unacceptable jitter

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Christopher D. Gill Real-Time ORBs

Future Work

– LynxOS offers low latency and jitter (high predictability) – VxWorks does also, with small number of low-priority clients; but does not scale well – Non-RTOS’ have high latency and/or jitter

– Fairly consistent results across platforms

– Ranges from under 3 percent (Windows NT) to over 17 percent (VxWorks)

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Concluding Remarks

– Dynamic and hybrid scheduling of requests and operations – Specifying QoS requirements – Distributed QoS and integration with real-time I/O Subsystems – Alleviating priority inversion and non-determinism – Reducing latency/jitter for demultiplexing – Reducing presentation layer overhead – Optimizing IDL compilers – Maintaining small footprint

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For Further Information

– Demultiplexing latency:

www.cs.wustl.edu/

– SII throughput:

www.cs.wustl.edu/schmidt/SIGCOMM-96.ps.gz

– DII throughput:

www.cs.wustl.edu/schmidt/GLOBECOM-96.ps.gz

– Latency, scalability:

www.cs.wustl.edu/schmidt/ICDCS-97.ps.gz

– IIOP:

www.cs.wustl.edu/schmidt/IIOP.ps.gz

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Christopher D. Gill Real-Time ORBs

For Further Information

www.cs.wustl.edu/

www.cs.wustl.edu/

www.cs.wustl.edu/schmidt/TAO.ps.gz

www.cs.wustl.edu/levine/research/scheduling/dynamic.pdf

www.cs.wustl.edu/schmidt/RT-middleware.ps.gz

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Christopher D. Gill Real-Time ORBs

For Further Information

www.cs.wustl.edu/

www.cs.wustl.edu/

www.cs.wustl.edu/

www.cs.wustl.edu/

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