User + sys times greater than elapsed time

Posted in 2005

mweallans@panacea.co.uk — 30 Sep 2005 10:29:33 -0700 — source: Usenet: comp.databases.informix

Previously in these hallowed halls I have queried the values for user and sys cpu as reported by sysmaster. The documentation says that it reports minutes but I have proved that it is seconds. The today I hit another "strange effect". I have been trying to look into a performance problem so I have written a script which basically selects user and os times from the sysmaster database and stores them with the current time. I run this script at 10 minute intervals throughout the day. Imagine my surprise when I find that user time + sys time comes out to greater than elapsed time * number of processors. Does anybody have any idea why? regards Malcolm

↪ replying to mweallans@panacea.co.uk

Madison Pruet — Fri, 30 Sep 2005 14:05:40 -0500 — source: Usenet: comp.databases.informix

Because the times are measured in units of CPU clock ticks, not as a continuum ;-) Here's the problem. If the length of the clock tick is measured as a finite unit (which it is), then how can you split that unit? (you can't). So if the control changes from a user control to the kernel control within a clock tick as opposed to the cusp of the clock tick, then the time measured is going to be a bit fuzzy because both the system and the user will be granted that clock unit, eventhough the system only used a percentage of the clock tick and the user used the other part. IDS gets it's breakdown from the same place that timex. <mweallans@panacea.co.uk> wrote in message news:1128101373.096285.235770@o13g2000cwo.googlegroups.com... > Previously in these hallowed halls I have queried the values for user > and sys cpu as reported by sysmaster. The documentation says that it > reports minutes but I have proved that it is seconds. > > The today I hit another "strange effect". I have been trying to look > into a performance problem so I have written a script which basically > selects user and os times from the sysmaster database and stores them > with the current time. > > I run this script at 10 minute intervals throughout the day. Imagine > my surprise when I find that user time + sys time comes out to greater > than elapsed time * number of processors. > > Does anybody have any idea why? > > regards > > Malcolm >