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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Member since:

I would bet any amount of money the Ubuntu page is wrong.

"Hard real time" isn't a vague descriptive phrase. It's an actual concept used to describe ultra-strict time constraints where something not happening exactly when it needs to has severe consequences like an explosion or people dying. It's used in stuff like nuclear power plants, avionics, etc.

Soft real time systems are those that have strict timing requirements, but missing a deadline isn't too big a deal. Playing an MP3, for example, requires refilling the audio buffer before the old one is consumed, but it's not the end of the world if it doesn't happen.

It takes a whole lot of work to make a large hard real time system, and it just doesn't make sense to put in the effort for a desktop system.

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Redeeman Member since:

yess, well... Linux isnt just for desktops, even though this is one of its best uses ;)

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jlarocco Member since:

But Ubuntu is aimed squarely at the desktop.

If anybody is going to make a hard real time version of Linux, it's probably not going to be them.

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philicorda Member since:

'hard' real time is not so well defined as you might imagine.

A truly deterministic implementation cannot have such niceties as processor cache, interrupts or file i/o as you cannot accurately predict their latencies.

A practical 'hard' real time system still has to allow for missed deadlines, or have some kind of priority assignment for real time threads. This opens up the possibility of priority inversion. (see Mars Rover Pathfinder.)

So there are always compromises and each implementation is specific. The Linux RT patches provide one implementation, with all the problems associated with running on commodity hardware, networking, file io etc. Whether it fits your needs is another matter.

Reply Parent Score: 1