On Sun, 13 Aug 2006 12:46:35 +0200 Dominique Michel <[EMAIL PROTECTED]> wrote:
> A rt kernel will be of almost no use if you don't fix the priorities. > You can use PAM-rlimits or the realtime-lsm module for that, and you > have to be in the audio group. > > The audio group will have a higher priority and this is the right way > to do that. > > You can take a lock at > http://demudi.agnula.org/wiki/Low-latencyKernelBuildingHowto#Realtimescheduling > > PAM-rlimits is the new way of doing that, but if you want an very > low latency for intensive audio work as synthesis or filter, the > realtime.lsm will be better. There's no difference wrt to achievable latencies regarding lsm and pam. Both are just ways to grant non root users SCHED_FIFO priorities for their tasks. > A very important issue with a rt kernel is at you must not have shared > IRQ with a such kernel. You can check it with > # cat /proc/interrupts > It is specially important for the sound and the video card. > http://ardour.org/system_requirements This is also not true stated like that. It is very well possible to have shared IRQ's in a -rt system. Usually one doesn't want to have one's soundcard IRQ shared though, because then the other device driver [and irq handler] runs at the same prio potentially causing delays for out soundcard. > > If you are new with rt-kernel, I would recommend you to install an > audio distribution as Demudi, planet CCRMA, jacklab, musix, or the > gentoo audio pro overlay. They all have that rt stuff trimmed for you. > > With usb audio card, the IRQ period of the USB bus is 1 msec. That > mean at you must use something as 48KHz 3 periods with jack (That will > be a multiple of that irq period) in order to get a low > latency with such sound cards. > And you MUST NOT be root in all cases with a rt-kernel. This is also not true. Of course it is possible to run your stuff as root with a -rt kernel. This also saves you the hassle of setting up either the realtime lsm or pam. But it is not recommended as running user stuff as root is often a security risk. Flo -- Palimm Palimm! http://tapas.affenbande.org
