1. CS533 Concepts of Operating Systems Class 18 Fine Grain Timing

2. 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??

3. 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?

4. 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?

5. 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?

6. 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. "A Measurement-Based Analysis of the Real-Time Performance of the Linux Kernel,"  "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. "Real-Rate Scheduling,"  "Operating System Support for Low-Latency Streaming" Ashvin Goel, Ph.D. Thesis, OGI School of Science and Engineering, OHSU, July 2003. "Operating System Support for Low-Latency Streaming"