Star Finally, Secure Real-Time on the Desktop
Linked by David Adams on Fri 18th Apr 2008 17:34 UTC, submitted by Rahul
Linux Lennart Poettering of Red Hat, PulseAudio maintainer has blogged in detail about the impact of Real-Time Group scheduling in 2.6.25 kernel. The Real time patches come from -rt patchset maintained by Ingo Molnar of Red Hat which aims to make Linux the first general purpose operating system with hard real time features.
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tomcat
Member since:
2006-01-06

Some of the documents I refer specifically use the word hard real time. As an example


Regardless of the document's use (or misuse) of the term "hard realtime", it's a well understood fact that hard realtime means guaranteed deadlines; unless the Linux kernel provides microsecond accuracy, it's "soft realtime". This isn't a fuzzy definition -- or a minor distinction -- hard realtime guarantees are required particularly for systems where subtle variations in performance or latency can have tragic consequences (eg. flight control systems, etc).

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Rahul Member since:
2005-07-06

The vanilla kernel doesn't but we are talking about -rt patchset specifically and you can read about their goals in the kernel wiki and read about the exact guarantees within specific products offered by vendors using this patchset.

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ichi Member since:
2007-03-06

I was under the impression that hard real-time meant just guaranteed deadlines with no drop in service quality, nothing to with whether it guaranteed one or several microseconds.

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Rahul Member since:
2005-07-06

You are correct. Hard real time does not mean fast. Merely a guarantee to do a particular transaction within a particular time slice. In fact, enabling hard real time can make your general performance go down in preference to less spikes.

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sbergman27 Member since:
2005-07-24

it's a well understood fact that hard realtime means guaranteed deadlines; unless the Linux kernel provides microsecond accuracy, it's "soft realtime".

You contradict yourself, here. If hard real time means guaranteed deadlines (and it does) what do "microseconds" have to do with it? The guarantee could be that it will definitely do something within one millisecond, or one year, but if it can be even one Planck Time over that, it fails the test. The definition of hard real time is, in fact, so pedantic, that I think I can say with reasonable certainty, that nobody, except maybe God, legitimately needs it.

In short, I think there's a Universal market of maybe 1 real time computer. And you can quote me on that. ;-)

Edited 2008-04-19 19:52 UTC

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tomcat Member since:
2006-01-06

The definition of hard real time is, in fact, so pedantic, that I think I can say with reasonable certainty, that nobody, except maybe God, legitimately needs it. In short, I think there's a Universal market of maybe 1 real time computer. And you can quote me on that. ;-)


Try to remember that the next time you're riding on a plane and you're approaching for landing. Or, when you need to stop suddenly in your car. Or, when a nuke plant operator needs to regulate cooling. Because those are scenarios where it's needed.

Edited 2008-04-19 23:12 UTC

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