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My response only got sent to Fernando. Here it is for all of you to see :)
/Lars
---------- Forwarded message ----------

From: Lars-Erik Helander

Date: 2009/2/2

Subject: Re: [LAT] [LAU] Are RT-patches needed anymore? (Was Re: >=

2.6.27 RT  ETA?)

To: Fernando Lopez-Lezcano 
Fernando your elaborate response is highly appreciated, thanks!!
>>   - Will "rtirq" make a difference on a non-RT-patched kernel system?

quoted text
>

> No AFAIK. Non-rt patched kernels do not have irq processes running as

> separate SCHED_FIFO threads (which is what is tuned by rtirq).

>

This was my thought to.

>>   - Do I need to assign rtprios explicitly to all my processes

quoted text
>> (qjackctl, qsynth, ...) or is that "automagic"?

>

> Automagic. Jackd gives the proper priority to the clients (to the thread

> of the client that handles audio i/o)

>

I use "lmms" every now and then. I have never been able to get "lmms"

to work well with jack so I use it with ALSA as the audio driver. This

works fine though I can not use jack application simultaneously. So in

this case do I have to explicitly give "lmms" SCHED_FIFO and rtprio?

How (using chrt?) ?

>> I have close to 30 years experience in developing realtime systems and

quoted text
>> has been using Linux for audio in various distribution the last two

>> years. Further I have built RT-kernel for couple of distributions

>> (this weekend I successfully built and ran a 2.6.28-rt kernel from the

>> new git tree :) ).

>

> Ah, I have not tried this yet! How did that work out? Any errors or

> problems on boot? How exactly did you go about building the whole thing?

>

About a week ago building from the git produced a kernel that did not

boot properly, actually it did not even build properly and my own

remedy for the build problem resulted in a kernel that was not able to

boot up properly. However building from the git this weekend produced

a well working kernel. Only problem found is the softirq.c bug that

has been around for a while (it makes USB MIDI keyboards etc not to

work - they are discovered but no MIDI events are received) so I had

to apply a patch for that problem.

Build procedure was very straightforward using the git url I cloned

the git and got myself a complete (already "patched" kernel source

tree) and it was just to do the normal "make oldconfig", "make

menuconfig" ... procedures.

>> However I have no experience in using newer non-RT

quoted text
>> kernels but I am very interested to find out how well you can have

>> them work, especially since whenever you find a nice distro you can

>> not use it because the hazzle of building an RT-kernel for that

>> particular distro is so big :(.

>

> Planet CCRMA (http://ccrma.stanford.edu/planetccrma/software/) has rt

> patched kernels of the 2.6.26.8* flavor for fc9 (in the "testing"

> repository) and fc10, and should be easy to install (not an objective

> assessment, I created and maintain Planet CCRMA :-).

I have also sucsessfully built and used 2.6.26.8-rt13 with the Slitaz

(www.slitaz.org) distribution (the git kernel also works with that

distribution).

In order to use the kernel with my USB MIDI devices I had to apply the

above mentioned softirq.c patch.
/Lars

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