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#1 2008-10-31 19:20:09

ioky
Member
Registered: 2008-06-19
Posts: 93

What is the difference between normal kernel and real time kernel?

I have use Linux for a while, and never question about it. And Now, I finally realize the question is there.

So, what the difference a normal kernel and a real time Kernel (rt)? and what difference do they make.

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#2 2008-10-31 19:32:41

Wintervenom
Member
Registered: 2008-08-20
Posts: 1,011

Re: What is the difference between normal kernel and real time kernel?

I beleive it has to do with latency.  A real-time kernel tries to get rid of as much latency as possible.  It is important in applications such as audio, where, for example, someone wants to record while playing along with audio they're playing.

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#3 2008-10-31 20:18:44

scrllock
Member
From: Michigan, USA
Registered: 2008-06-04
Posts: 19

Re: What is the difference between normal kernel and real time kernel?

The realtime kernel is intended more for industrial and embedded applications, where the linux system is interfacing with some object moving around in real space. You probably won't ever need or have to use a realtime kernel, unless you're designing some sort of mission-critical linux robot or something else along those lines. For normal server/desktop performance, the non-rt kernels are much more catered to your needs.

http://www.linuxdevices.com/articles/AT9837719278.html

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#4 2008-11-01 00:23:56

Mr.Elendig
#archlinux@freenode channel op
From: The intertubes
Registered: 2004-11-07
Posts: 4,092

Re: What is the difference between normal kernel and real time kernel?

rt kernels are nice to have if you are doing audio/video stuff....


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#5 2008-11-01 01:12:00

denisfalqueto
Member
From: ES, Brazil
Registered: 2006-03-24
Posts: 197

Re: What is the difference between normal kernel and real time kernel?

Probably you're talking about the real time patch, by Ingo Molnar. This patch makes the kernel behave as a soft real time kernel. This means that it handles interrupts faaster than a normal kernel, but is still not a hard real time kernel, meaning that it can't commit to a time deadline for every hardware interrupt.

The patch achives that by removing a kernel lock and replacing it with spin locks, if I'm not mistaken, enabling the kernel to be interrupted in places that it couldn't be normally. This makes it handle the hardware events much faster than a normal kernel would. That's why many people say that is necessary to use a realtime kernel for audio and video recording and editing. Is important to say that some well made hardware does not need obligatoryly to be used with a real time kernel. But some, such as usb audio cards, really are handled much better with a rt kernel.

Funny you asking about that. For example, I just received my Echo Indigo IO sound card. I tested it today with the standard linux kernel and I got some very decent latency (such as 5 or 6 miliseconds) without any kernel modifications. The test was not perfect, because the X Server was (still is...) grabbing the CPU constantly whtount any reason.

So, if you are considering a real time kernel, do a good research to see if you realy need one.


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