[PD] [OT] linux preempt kernel vs rt kernel

[Pedro Lopes]

UbuntuStudio is an official rt kernel with 64 bits. You do not need to
compile your own. rt kernels are not at the same stage as the generic, I
never noticed any issue or problem with rts. But its your call.

I have two rt's, my first was Ubuntu Studio 64 bits, and later I pacthed my
Ubuntu Karmic 32 bits to be rt. It also stores all the other kernels, you
don't loose the generic ones and you can boot from them anytime, grub adds
every kernel image to the boot (you'll have the rt and the generic side by
side at boot). Don't worry.

This is my kernel version, on the 32 bits:
pedro at arkana:~$ uname -a
Linux arkana 2.6.31-9-rt #152-Ubuntu SMP PREEMPT RT Thu Oct 15 05:01:14 UTC
2009 i686 GNU/Linux


2010/6/30 András Murányi <muranyia at gmail.com>

> The point is that the newest kernel versions are not available in rt
> flavour (the latest is 2.6.31-11 and my experiences were not good with it).
> This is first time i heard about the lowlatency flavour, but it's not in my
> Ubuntu repos.
> So i'm afraid, if i want a new rt kernel (for 64-bit...), i'll have to use
> a ppa or build my own.
>
> Andras
>
> 2010/6/30 Pedro Lopes <pedro.lopes at ist.utl.pt>
>
> What?
>>
>> Of course not. Its a pacth - no compiling needed. But be sure to keep a
>> generic kernel at the boot (just use grub to preserve a boot without rt, I
>> never had problems and use the same rt kernel for 1 year, but safety first
>> =P)
>> Real time (-rt) and Low latency (-lowlatency) kernels
>>
>> You may want to install the -lowlatency kernel, you can simply do:
>>
>>  sudo apt-get install linux-lowlatency linux-headers-lowlatency
>>
>> If you still experience Xruns or you have a firewire sound card supported
>> by the FFADO project, you may want to install the -rt kernel:
>>
>>  sudo apt-get install linux-rt linux-headers-rt
>>
>>
>>
>> 2010/6/30 András Murányi <muranyia at gmail.com>
>>
>> Buh, it seems then i'll need to get a kernel from a PPA or compile it
>>> myself. A bit afraid of it, honestly.
>>> Thanks for the explanation!
>>>
>>> Andras
>>>
>>>
>>> On Sat, Jun 26, 2010 at 12:50 PM, Ricardo Lameiro <
>>> ricardolameiro at gmail.com> wrote:
>>>
>>>> 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 at 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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-- 
Pedro Lopes
contacto: jazz at radiozero.pt
website: http://web.ist.utl.pt/Pedro.Lopes
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