On Mon, 2007-03-12 at 01:06 +0100, Chitlesh GOORAH wrote: > Last weekend, I talked to someone at Cheminitz Linuxtag who was > interested with real time music editing on desktop computers. I was > unable to answer him whether he can use fedora kernels to do so or to > use the CCRMA's kernel. > > Can anyone shed any light on this light . I'll mail him with the answer > > Chemnitz Linuxtag: my report: > http://clunixchit.blogspot.com/2007/03/chemnitz-linuxtag-my-report.html#links > > He was quite interested with the article > http://www.redhatmagazine.com/2007/02/15/professional-audio-with-fedora-core-6/ The stock Fedora Core kernel is usable if you don't have requirements for low latency (ie: if you are not working, for example, with instruments you want to trigger in realtime). Probably running Jack with the default 1024 frame buffers is going to work (at least most of the time) but that translates into a roundtrip latency of about 42mSec at 48KHz, hardly "realtime". If you want the best realtime performance it is not going to be enough. Which means you will get xruns if you use it, more or less of them depending on your hardware and sofware configuration. The Planet CCRMA kernel is stock linus plus Ingo Molnar's realtime preemption patches configured with PREEMPT_RT, which offers the best low latency performance but might still suffer from problems in specific hardware configurations - there's a lot of broken hardware out there and in some cases you may not be able to boot or may have to, for example, turn off acpi, but that has not happened to me lately in my limited tests. So, for low latency you should use that (either from the Planet CCRMA repo or directly from Ingo's repo). The Planet CCRMA core packages add a few things other than the kernel. The realtime preemption patch splits the interrupt request handling in two parts, the lower half of them running at SCHED_FIFO priority. For best performance you should tune your interrupt scheduling priority so that your soundcard (and related hardware) has the highest, Jack itself is in between, and the rest of the interrupts are below Jack in priority (it is more complicated than that but you get the idea). For that Planet CCRMA adds the "rtirq" startup service (by Rui Nuno Capella) that tunes the interrupts at boot time. In addition the Jack package in Planet CCRMA tweaks jackd to run with a basic priority of 60, which fits with the realtime preemption patch defaults and the tuning done by rtirq. This won't make a difference if you boot into the Fedora kernel but tunes the realtime preemption system for best performance. Last but not least, if you want to run jackd with realtime priority (the only sensible way to run it in either kernel) as a non root user you need to tweak /etc/security/limits.conf. Planet CCRMA includes a patched pam that automatically grants all users permission to lock memory and use SCHED_FIFO (and, of course, DOS the machine if they want to :-). That's about it, I think. As of a few days ago you can install the whole sheebang (if you are pointing to the Planet CCRMA repo) on i386[*] with "yum install planetccrma-core". Hope this helps clarify things a bit more... -- Fernando [*] I still have to do pam packages for x86_64, other than that it installs as well. _______________________________________________ Fedora-music-list mailing list Fedora-music-list@xxxxxxxxxx http://www.redhat.com/mailman/listinfo/fedora-music-list
