Fwd: [LAU] Are RT-patches needed anymore? (Was Re: >= 2.6.27 RT ETA?) - Linux-audio-tuning

2 Feb 2009

My response only got sent to Fernando. Here it is for all of you to see :)

/Lars

---------- Forwarded message ----------
From: Lars-Erik Helander &lt;lehswe(a)gmail.com&gt;
Date: 2009/2/2
Subject: Re: [LAT] [LAU] Are RT-patches needed anymore? (Was Re: >=
2.6.27 RT  ETA?)
To: Fernando Lopez-Lezcano &lt;nando(a)ccrma.stanford.edu&gt;

Fernando your elaborate response is highly appreciated, thanks!!

...
     - Will
"rtirq" make a difference on a non-RT-patched kernel system? 
 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
 (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
 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
 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