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atrus123
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PostPosted: Thu Aug 24, 2006 12:29 pm    Post subject: Real Time Linux? Reply with quote

http://www.internetnews.com/dev-news/article.php/3627831

I don't really understand this. So some processes will take precedence over others, depending on user commands? Say, I open amaroK while the system is setting the clock, and it decides to wait on the clock to get me amarok faster? Or is there more to it than that?

In any case, it sounds like good news for Linux, and it also sounds like it isn't far off.
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PostPosted: Thu Aug 24, 2006 12:44 pm    Post subject: Reply with quote

it rather sounds like marketing babble. real time usually means less kernel overhead... or rather: no kernel overhead, i.e. no context switches and stuff, the application runs directly on the cpu without the kernel distributing cpu time between tasks. ( dos used to work like that, you'd talk to the OS using interrupts (you still do with linux, actually). the kernel didn't get in your way, but you could call it using interrupts, then it'd take over, do it's thing and return to the application. )

real time with linux could get tricky though, because of things like multitasking (can't have that without context switches; and you can't have context switches and real time at the same time). unless... on SMP systems it could work. you could run an application on one CPU exclusively and have all other tasks run on a different CPU.
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vibrokatana
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PostPosted: Thu Aug 24, 2006 2:46 pm    Post subject: Reply with quote

I believe it was developed for audio/video recording in linux where the 20-100ms delay is not really usable... that allows for <1ms of delay.

OSX also has a realtime audio layer.. the article sounds interesting, now where is our 2.8 kernel with real time processing?
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Tekel
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PostPosted: Thu Aug 24, 2006 2:56 pm    Post subject: Reply with quote

vibrokatana wrote:
I believe it was developed for audio/video recording in linux where the 20-100ms delay is not really usable... that allows for <1ms of delay.

OSX also has a realtime audio layer.. the article sounds interesting, now where is our 2.8 kernel with real time processing?


This is mostly true Real Time OS's have been around for a while, and there have been Real Time Linux patches for quite some time too. I do beleave that it simply reduces the maxium latency going through the kernel. Like if i say I need foo now. In the worst case seranio it will happen X ms after I call it. That was a very simplistic explenation. I will let Wikipedia do the hard talking

Wikipedia entry on RTOS
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aidy
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PostPosted: Thu Aug 24, 2006 3:17 pm    Post subject: Reply with quote

um... we already have realtime through linux security modules, that page is blahblah

Realtime basically means that system calls get executed near the moment the program running in realtime mode calls them. ( I think )
This is very handy for audio-studio apps that need response on the exact moment a signal is given etc.
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PostPosted: Thu Aug 24, 2006 4:16 pm    Post subject: Reply with quote

http://vipernicus.evolution-mission.org/patches/2.6.17/nicus1/patches/

Here are some kernel patches with full preemption/realtime in it. Apply them in order.
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hellbringer
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PostPosted: Thu Aug 24, 2006 6:23 pm    Post subject: Reply with quote

Aidy wrote:
um... we already have realtime through linux security modules, that page is blahblah

Resisr4 is also a module but if it got it's way inside the kernel it would be news.

Aidy wrote:

Realtime basically means that system calls get executed near the moment the program running in realtime mode calls them. ( I think )

No. There is truly no easy description for RT (hard/soft, etc) but it basically means that you have a time critical code that needs to be run in a fixed interval of time (we are usuallytalking at microsecond level here) or shit happens. A system that can "guarantee" it is going to do the best to fulfill the requirement is called a RT system.

Actually this is great news because it will boost Linux in the embeded market which is probably the most important market in growth terms of the moment.
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Tekel
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PostPosted: Thu Aug 24, 2006 6:54 pm    Post subject: Reply with quote

Aidy wrote:
um... we already have realtime through linux security modules, that page is blahblah

Realtime basically means that system calls get executed near the moment the program running in realtime mode calls them. ( I think )
This is very handy for audio-studio apps that need response on the exact moment a signal is given etc.


You are almost competly incorrect.
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aidy
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PostPosted: Thu Aug 24, 2006 7:46 pm    Post subject: Reply with quote

kewl!
yeh i know shit
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vibrokatana
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PostPosted: Thu Aug 24, 2006 7:55 pm    Post subject: Reply with quote

I think they are just wrong on how it is implemented..

The actual use is one application for it
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PostPosted: Thu Jan 04, 2007 5:21 pm    Post subject: Reply with quote

I hate to drag old threads up, but Ive got a few questions.

RTOS:
a good all-encompassing article? (I am no computer scientist... so keep that in mind)

I want to optimize a single threaded simulation suite that I run, if I run it over a real-time linux solution (help me here...) will I be able to get the most out of my hardware for this one application?


My understanding goes like this: since I only want to run a simulation (number crunching, floating point, very high precision needed, no graphics) and nothing else, I could use a real-time linux solution, like the patches available for 2.6 kernel, and get the most resource commitment to my simulation, allowing a slightly faster turnaround between simulations?
oh and do those real-time solutions via patches work for amd64?

I am lost with this real-time concept, please help. thanks.
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feld
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PostPosted: Thu Jan 04, 2007 7:25 pm    Post subject: Reply with quote

vipernicus wrote:
http://vipernicus.evolution-mission.org/patches/2.6.17/nicus1/patches/

Here are some kernel patches with full preemption/realtime in it. Apply them in order.



Real Time patches were merged into 2.6.19. Go into the kernel config and enable them.
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