linuxaudio.org

On Thursday 22 December 2005 07:29, Hector Centeno-Garcia wrote:

quoted text
> One aspect that I haven't understood completely is the setting

> of priorities both in Jack and the IRQs. I've tried following the

> instructions at the tapas web site using | chrt -f -p 99 `pidof |but I

> can't notice any difference in the performance (using a complete

> preemtion kernel).

I've been fiddling with Ingo's 2.6.14-rt patches (kernel config, e.g.,

PREEMPT_DESKTOP vs PREMPT_RT, RCU prempt, etc., and then at run-time:

priorities, PCI bus latencies, threading/unthreading IRQ's, etc.) for a week

or so, trying them out on a small collection of hardware  (intel AC'97,

Emu-APS, USB UA-25, freebob+FA-66 and firebox) and i've gotten baffling

results now and then. For the AC'97, for instance, rt-patched and non-patched

(yet preempted) kernels perform neck and neck (jackd with 32 frames/period

perfectly stable), while for other (esp. freebob) cards, a completely

preempted kernel eventually won out in an undisputable way (after tough

tweaking of IRQ's though!)... I've just started writing things out neatly and

i'm planning to release my whole set of measurements on line by next week,

for that matter.
But my general feeling so far is probably that of Florian: whenever complete

(i.e., PREMPT_RT) preemption works, it works real great, and it's definitely

worth giving it a try. Now, in view of the large set of possible low-latency

kernel/system parametrization, it comes as no surprise that experimenting is

more mandatory than ever...
Syd