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CS533 Concepts of Operating Systems Class 18

CS533 Concepts of Operating Systems Class 18. Fine Grain Timing. 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? What if the application doesn't make any system calls?

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CS533 Concepts of Operating Systems Class 18

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  1. CS533 Concepts of Operating SystemsClass 18 Fine Grain Timing

  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? • What if the application doesn't make any system calls? • What other kernel events can be used? • Can timer checks be inserted elsewhere?? CS533 - Concepts of Operating Systems

  3. Questions • What is the main source of overhead for device interrupts? • Can they be taken at more convenient times? • Can they be batched? • Why not turn off interrupts and just poll for I/O? • Why not batch timer events? • How can you take only the ones you need? • 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? • how are the cost of interrupts related to the cost of synchronization instructions ? • how will increased parallelism affect this problem? • Why does kernel preemptability affect timing accuracy? • how can preemptability be improved? CS533 - Concepts of Operating Systems

  5. Questions • What is temporal protection? • 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. CS533 - Concepts of Operating Systems

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