22 Dec
2005
22 Dec
'05
10:19 a.m.
On Thursday 22 December 2005 07:29, Hector Centeno-Garcia wrote:
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