On Mon, 2010-05-24 at 09:02 +1000, Peter Chubb wrote: > Actually it doesn't give the whole answer.
Wow, thanks heaps Peter. tenzero: so there are 1000 (CONFIG_HZ) samples per second. For each sample your program is one of: not scheduled, running in user, running in system, or has yielded the processor due to a blocking event such as I/O or an explicit sleep(). It is possible that all processes yield and you get scheduled twice in one sample -- I'd note that, and then ignore the possibility. Run an infinite loop in another process if it worries you. That bastard will never yield, and so your process will never be scheduled twice in a tick. If you have multiple CPUs, bind one infinite loop to each CPU. In reality, unless your results are odd, this is a lot of work to exclude an unlikely case. With luck, your program is such that you can use strace to count the blocking events on a single run of your program. Then pretend that the scheduler tick misses every one of these. So if you program has 10 blocking events and runs for 1.00 second then there result has a bound of [1.00, 1.01]. Including the reporting error from the API [0.99, 1.02]. You will save yourself a world of statistics if your "better" program's range falls completely under the "worse" program's range. In your Appendix you acknowledge Peter's contribution with a footnote (eg, "Thanks to Dr Peter Chubb of UNSW for explaining the sampling nature of the Linux task accounting"). In general, you don't cite these sort of e-mail discussions since they are "all care and no responsibility" discussions rather than a considered opinion ready for peer review. Of course, where the posting becomes a part of the record (such Linus's announcement of Linux) then you reference. You will see from this discussion the common research hassle that determining the error of an experiment is usually more work than determining the result. Best of luck with your studies, Glen -- Glen Turner Australia's Academic & Research Network (AARNet) www.gdt.id.au/~gdt -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
