CS533 Concepts of Operating Systems Class 18
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Transcript of CS533 Concepts of Operating Systems Class 18
CS533 Concepts of Operating Systems
Class 18
Fine Grain Timing
CS533 - Concepts of Operating Systems 2
Questions
What is the main source of overhead for hard timers?
Why does it help to use soft timers?
How frequently do soft timers fire? o What if the application doesn't make any system calls?o What other kernel events can be used?o Can timer checks be inserted elsewhere??
CS533 - Concepts of Operating Systems 3
Questions
What is the main source of overhead for device interrupts?
o Can they be taken at more convenient times?o Can they be batched? o Why not turn off interrupts and just poll for I/O?
Why not batch timer events?o How can you take only the ones you need?o Why do soft timers help one shot timers?
CS533 - Concepts of Operating Systems 4
Questions
What is the main source of timing error in Linux?
Why hasn't timer frequency increased in line with CPU speed?
o how are the cost of interrupts related to the cost of synchronization instructions ?
o how will increased parallelism affect this problem?
Why does kernel preemptability affect timing accuracy?
o how can preemptability be improved?
CS533 - Concepts of Operating Systems 5
Questions
What is temporal protection?o Does proportion period scheduling support it?
Why might you need a feedback controller above a proportion period scheduler?
CS533 - Concepts of Operating Systems 6
For more information …
See the following papers available at:http://www.cs.pdx.edu/~walpole/
"A Measurement-Based Analysis of the Real-Time Performance of the Linux Kernel,"
Luca Abeni, Ashvin Goel, Buck Krasic, Jim Snow, and Jonathan Walpole, in Proceedings of The 8th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS 2002), San Jose, California, September 2002.
"Real-Rate Scheduling," Ashvin Goel, Molly Shor and Jonathan Walpole, in Proceedings of the 10th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS 2004), Toronto, Canada, May 2004.
"Operating System Support for Low-Latency Streaming"
Ashvin Goel, Ph.D. Thesis, OGI School of Science and Engineering, OHSU, July 2003.