>>>>> "tenzero" == tenzero <tenz...@iinet.net.au> writes:
tenzero> Hi everyone, I'm seeking a preferably citeable reference to tenzero> the amount of error in the returned result from a Time() tenzero> command. I want to be able to quote the level of error in tenzero> timing the execution speed of my project. Do you mean time(2) ??? Short answer: it depends. Long answer: time(2) returns the number of seconds since the epoch. It's accurate for timing in the absence of leap-seconds, and jumps caused by NTP etc. But it can go backwards, and forwards by more than one step at a time. For details, see time(7). If you want accurate timings, use one of the POSIX monotonic clocks. man 3 clock_gettime and look for CLOCK_MONOTONIC Also, you are aware (I assume) that how long something takes depends not only on its own processing time, but on how much else is happening on the system? You can measure just your own process (and its children's) times using the times() system call; if the kernel has been compiled with CONFIG_VIRT_CPU_ACOUNTING time spent in interrupts will not be included in your times. This isn't such an issue on BSD-derived systems such as MacOSX, because they use separately scheduled threads for interrupts. -- Dr Peter Chubb http://www.gelato.unsw.edu.au peterc AT gelato.unsw.edu.au http://www.ertos.nicta.com.au ERTOS within National ICT Australia -- SLUG - Sydney Linux User's Group Mailing List - http://slug.org.au/ Subscription info and FAQs: http://slug.org.au/faq/mailinglists.html
