2 Apr
2003
2 Apr
'03
8:30 a.m.
On 01 Apr 2003 22:57:28 -0500
Nick <nicktsocanos(a)charter.net> wrote:
I am writing audio applications that are real-time.
I had been using Port Audio which is really very good, even without root
priviledges, it does a very good job. I want to support other sound
drivers, in case someone doesn't have Port Audio or can't get it to
work.
I have just built my ALSA driver, it works ok, but I am getting terrible
latency problems and buffer underruns. The thing is it is a real-time
application, it must get audio to the card as soon as possible. Why is
it that OSS with Port Audio works so well, and my ALSA setup is
suffering?
Is there something I need to do to ALSA to get near real-time
performance from it? I have heard people mention patching their kernel
for low latency. I have Jack but I have not started working with it yet.
Should I dump ALSA and just go for Jack? Is there something I need to do
to my kernel to get better performance? I would get Planet CCRMA if it
supported my OS, but it doesn't, so I have to tweak my box manually.
High Nick !
At the moment there are two different approaches for low-latency in the
linux-kernel.
The first is from Ingo Molnar; it's quite simple but efficient (conditional
scheduling at critical places).
You can get it at
http://people.redhat.com/mingo/lowlatency-patches/lowlatency-2.4.0-test7-A0
The second is made by Robert Love, it makes real heavy Changes in the Kernel
which have a noticeable negative impact on overall System-througput, but the
results are quite amazing !
The Patch is integrated int the 2.5-Kernel (CONFIG_PREEMPT), patches for 2.4
are available at
ftp://ftp.kernel.org/pub/linux/kernel/people/rml/preempt-kernel/v2.4/
I use Robert's patch with the 2.5-Kernel since half a year without Problems;
The interactive response of the Sytem under high loads is now MUCH better.
Lacking real real-time Software i don't know if it helps there too.
If the low-latency patches for the Kernel don't cure your Problem, consider
testing a new 2.5.6x-Kernel; the scheduler was really improved in the last
months ...