well, AFAIK, the "RT" Kernel is a generic kernel that is modified by a special patch, that is made by Ingo Molnár. This patch gives the kernel the ability to have a behavior that allows the assignment of time frames and allocations to compute "rt" flagged tasks. Maybe this could be translated to the scheduler.In the other hand, the preemptive kernel, its a normal Generic kernel, that its compiled with different options. At compile time, the configuration of the scheduler and company are configured more aggressively to give a better response to the "rt" flagged apps.

As my opinion, that is worth nothing...., the preemptive kernels are comming into a very good level, since the main tree ot the generic kernel, has absorbing parts of Ingo's patches. But, still, the RT kernel is way more accurate on the scheduling etc. problem is that, RT kernels are in nature more Power hungry, and by the nature of its working, they could hang easily a computer, keeping only processing an high prio task.

If I said something wrong, please correct me, I have looked at this stuff since a year to try to understand it better, so if someone can explain it better, please do.

Ricardo Lameiro

2010/6/26 Andre "Osku" Schmidt <andre.osku.schmidt@osku.de>

On Fri, 2010-06-25 at 22:17 +0200, András Murányi wrote:
> Hello people,
>
> does anyone know what is the real difference between an 'rt' and a
> 'preempt' kernel in linux?

dunno, but here's a pretty interesting talk about real-time kernel
http://lac.linuxaudio.org/2010/recordings/day2_1045_How_the_Real_Time_Kernel_Helps_Audio_and_Video_Applications.ogv

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