"hard" real-time

Posted Nov 4, 2010 20:37 UTC (Thu) by dlang (guest, #313)
In reply to: "hard" real-time by dmarti
Parent article: KS2010: Deadline scheduling

even in the case of aircraft, missing one deadline does not make the plane crash. having the system lock up will make the plane crash, making the system miss deadlines too badly, or too frequently may make the plane crash.

there are _very_ few situations where a single missed deadline proves fatal to the system (or the user :-)

in engineering, the assumption is that you may have unexpected loads, or you may have sub-par materials, so every design includes a safety margin, which means that they make it statistically unlikely that too many things will go wrong and the item will fail.

Even on the Space Shuttle, something as critical as the heat resistant tiles are not individually critical, it's expected that some number of them will be damaged or fall off on any flight. When too many of them get damages, you have the Columbia disintegrating, but that doesn't translate into zero tolerance of tile failure

"hard" real-time

Posted Nov 4, 2010 22:26 UTC (Thu) by csimmonds (subscriber, #3130) [Link]

We seem to be getting off the topic here. The point is that Linux is used in real-time applications - I have worked on several myself. Real time is about determinism and deadlines, and typically there are a range of acceptable behaviours. Dead line scheduling is a valuable tool in designing systems that have to meet deadlines (in essence, it makes the analysis easier). So, it would make sense to have such a scheduler as an option in the Linux. People seem to be arguing against improving the kernel, and I don't understand why.

Chris.