Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!hplabs!hpda!hpdslab!hpiacla!scottg From: scottg@hpiacla.HP.COM (Scott Gulland) Newsgroups: comp.os.misc Subject: Re: Re: timeliness of real-time [was: Re: Realtime OS's] Message-ID: <6930001@hpiacla.HP.COM> Date: 13 Jul 88 15:20:26 GMT References: <4702@killer.UUCP> Organization: Hewlett Packard Lines: 27 > / hpiacla:comp.os.misc / stan@shell.com (Stan Hanks) / 10:18 am Jul 11, 1988 / > Just a quick question, while we're talking about realtime OS: > > what is the nominal interrupt dispatch time for Unix (time from the > the hardware interrupt line being yanked until your interrupt handler > is executing)? I can't remember that exact timing, but it is loooong. Something on the order of 2.0 milli-seconds on a totally quiescent system and 9.1 milli-seconds on a reasonable busy system. The averages are more like 0.8 and 1.3 milli-seconds respectively. Note that in real-time systems you should be asking for worst case rather than nominal. It does do much good if nine times out of ten that critical interrupt is handled just fine but on the tenth try you melted down your reactor because it took a hair too long to open a valve. These figures are for an HP9000/S840 running under HP-UX 2.0, a real-time Unix operating system. I am assumming that by interrupt handler you mean a user process for handling the interrupt. In this case the handler in these measurements is a real-time process which has the highest priority on the system. These measurements were taken using logic analyzers. ************************************************************************** * Scott Gulland | {ucbvax,hplabs}!hpda!hpiacla!scottg [UUCP] * * Indus. Appl. Center (IAC) | scottg@hpiacla [SMTP] * * Hewlett-Packard Co. | (408) 746-5498 [AT&T] * * 1266 Kifer Road | 1-746-5498 [HP-TELNET] * * Sunnyvale, CA 94086 USA | "What If..." [HP-TELEPATHY] * **************************************************************************