Linux RT newbie question

Linux RT newbie question

[David Aldrich]

Hi

For a new project we need to demonstrate a Linux RT-Kernel running on a 'standard' x86 desktop PC.

The question is which distro to use?  I am aware of commercially supported embedded distros from Wind River and Monta Vista.  However, as ours is not strictly an embedded target, I wonder if a standard Linux distro + RT kernel patch would be a better choice?

I have done some research and found the Planet CCRMA patches for Fedora and the Pengutronix patches for Debian.

Are there any other distros and patches that I should consider?  

Any advice on a way forward would be much appreciated.

Best regards

David

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Re: Linux RT newbie question

[Stanislav Meduna]

On 2/8/2016 1:16 PM, David Aldrich wrote:

> For a new project we need to demonstrate a Linux RT-Kernel
> running on a 'standard' x86 desktop PC.

What is the goal of this presentation? Are you aware that
a standard desktop PC might spoil your realtime attempts
in various ways (SMI interrupts, power management, ...)?

> I wonder if a standard Linux distro + RT kernel patch would be a better choice?

As long as you are using a RT kernel, sane pthreads support
such as modern glibc and you know what you are doing (ksoftirqd
priority and similar fun) the particular distribution does
not matter much. We are using stock Debian with custom kernel
as our embedded rt platform.

It is the _application_ that has to be coded with several things
in mind if it needs to be realtime.

-- 
                                 Stano

RE: Linux RT newbie question

[David Aldrich]

Hi Stano

Thanks for your reply ...

> > For a new project we need to demonstrate a Linux RT-Kernel running
> > a 'standard' x86 desktop PC.
> 
> What is the goal of this presentation? 

The goal is to demonstrate that a communication system previously implemented on embedded digital signal processors can be implemented on a high spec PC desktop. Sorry that I can't give more details.

> Are you aware that a standard desktop
> PC might spoil your realtime attempts in various ways (SMI interrupts, power
> management, ...)?

Well, I was not aware of this until reading your email and I read ' HOWTO: Build an RT-application' on rt.wiki.kernel.org. The HowTo suggests ways of reducing the impact of SMI interrupts. Is this possible?

> > I wonder if a standard Linux distro + RT kernel patch would be a better
> choice?
> 
> As long as you are using a RT kernel, sane pthreads support such as modern
> glibc and you know what you are doing (ksoftirqd priority and similar fun)
> the particular distribution does not matter much. We are using stock Debian
> with custom kernel as our embedded rt platform.

Do you build your kernel yourselves?

Best regards

David

Re: Linux RT newbie question

[Stanislav Meduna]

On 2/8/2016 3:28 PM, David Aldrich wrote:

> Well, I was not aware of this until reading your email and I read
> ' HOWTO: Build an RT-application' on rt.wiki.kernel.org.
> The HowTo suggests ways of reducing the impact of SMI interrupts.
> Is this possible?

I don't know - we are using industrial PCs so I don't really have
an experience with how big this problem is in reality on common
desktops. It also depends on what your deadlines are and how hard
they are (i.e. what happens if they are not met once in say
1000 calls).

> Do you build your kernel yourselves?

Yes, including some home-brew drivers and patches (none of them
specifically in the rt area) and stripped of features and drivers
not needed for the platform.

> I'm not sure that the audio community is the most appropriate
> for my application.

The audio community is most probably the largest group needing
realtime on common desktop hardware, so this is indeed a good
place to ask.

Regards
-- 
                                         Stano

RE: Linux RT newbie question

[David Aldrich]

Hi Stano and Ralf

> The audio community is most probably the largest group needing realtime
> on common desktop hardware, so this is indeed a good place to ask.

Thanks for your help.  I agree that I need to take a look at the audio community.

Best regards

David

AW: Linux RT newbie question

[Heinz Egger]

Hello David,

there are a number of well known and reputaded companies in the area of
digital audio, video or digital simulation (automotive), just to name a few
areas, which are using a standard PC, Linux and the Preempt-RT patch. With
latencies down to the single-digit microseconds region.  

So it is shown that Linux and realtime will work pretty fine here. 

br
Heinz

> -----Ursprüngliche Nachricht-----
> Von: linux-rt-users-owner@vger.kernel.org [mailto:linux-rt-users-
> owner@vger.kernel.org] Im Auftrag von David Aldrich
> Gesendet: Montag, 8. Februar 2016 15:28
> An: Stanislav Meduna; linux-rt-users@vger.kernel.org
> Betreff: RE: Linux RT newbie question
> 
> Hi Stano
> 
> Thanks for your reply ...
> 
> > > For a new project we need to demonstrate a Linux RT-Kernel running
> > > a 'standard' x86 desktop PC.
> >
> > What is the goal of this presentation?
> 
> The goal is to demonstrate that a communication system previously
> implemented on embedded digital signal processors can be implemented on
> a high spec PC desktop. Sorry that I can't give more details.
> 
> > Are you aware that a standard desktop
> > PC might spoil your realtime attempts in various ways (SMI interrupts,
> power
> > management, ...)?
> 
> Well, I was not aware of this until reading your email and I read ' HOWTO:
> Build an RT-application' on rt.wiki.kernel.org. The HowTo suggests ways of
> reducing the impact of SMI interrupts. Is this possible?
> 
> > > I wonder if a standard Linux distro + RT kernel patch would be a
better
> > choice?
> >
> > As long as you are using a RT kernel, sane pthreads support such as
modern
> > glibc and you know what you are doing (ksoftirqd priority and similar
fun)
> > the particular distribution does not matter much. We are using stock
> Debian
> > with custom kernel as our embedded rt platform.
> 
> Do you build your kernel yourselves?
> 
> Best regards
> 
> David
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Re: Linux RT newbie question

[Ralf Mardorf]

On Mon, 8 Feb 2016 12:16:03 +0000, David Aldrich wrote:
>Are there any other distros and patches that I should consider?  
>
>Any advice on a way forward would be much appreciated.

Hi,

yes there are, but this is the wrong place to ask.

Consider to send this request to

http://lists.linuxaudio.org/listinfo/linux-audio-user

Regards,
Ralf

RE: Linux RT newbie question

[David Aldrich]

Hi Ralf

> >Are there any other distros and patches that I should consider?

> yes there are, but this is the wrong place to ask.

I'm sorry if I am posting in the wrong place. I'm trying to find an applicable community where I can ask questions about RT Linux.

I'm not sure that the audio community is the most appropriate for my application.

Best regards

David

Re: Linux RT newbie question

[Ralf Mardorf]

On Mon, 8 Feb 2016 14:31:01 +0000, David Aldrich wrote:
>I'm not sure that the audio community is the most appropriate for my
>application.

My apologies David,

perhaps I'm mistaken and this list is the appropriated list for your
request. FWIW Linux CNC does use linux-rtai.

Regards,
Ralf