The perenial "Nuclear Power Plant" example [LWN.net]

The perenial "Nuclear Power Plant" example

Posted Oct 12, 2004 20:20 UTC (Tue) by darthscsi (guest, #8111)
In reply to: The perenial "Nuclear Power Plant" example by sbergman27
Parent article: Approaches to realtime Linux

Hard realtime has nothing to do with *fast*, just deturministic response. If I can write a system that always has bounded latency of 1 hour, then I am in the hard realtime realm (though not useful really). If I have a system that has average latency of .00000001 nanoseconds, but on some pathalogical cases cannot be anylized, then we are out of the deturministic (hard realtime) realm, no matter how much faster this second system is.

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The perenial "Nuclear Power Plant" example

Posted Oct 12, 2004 21:08 UTC (Tue) by hppnq (guest, #14462) [Link] (2 responses)

But the deterministic response follows from the speed at which operations can take place.

The perenial "Nuclear Power Plant" example

Posted Oct 12, 2004 23:22 UTC (Tue) by gilb (subscriber, #11728) [Link] (1 responses)

Nope, it isn't speed, it the ability to specify an upper bound to the response time that is required for deterministic operation. You need to be able to complete your desired task as well (which relates to speed), but the deterministic requirement simply states that you will always have to the opportunity to do your task every N time intervals.

For example, in a modern plane like the B2 or JSF, you may need to adjust the control surfaces every 10 ms in order to guarantee stable flight. You know that this will work because you ran the simulations that showed that 10 ms will work. If the response time exceeds this, the plane may be stable or it may not be, but you don't want to find out while it is flying.

The perenial "Nuclear Power Plant" example

Posted Oct 13, 2004 10:20 UTC (Wed) by hppnq (guest, #14462) [Link]

You need to be able to complete your desired task as well (which relates to speed)

That's what I mean.