[linux-audio-user] alsa rme96 jack - 186 msec latency?

Paul Davis paul at linuxaudiosystems.com
Wed Sep 14 16:20:53 EDT 2005


On Wed, 2005-09-14 at 20:51 +0200, Georg Rudolph wrote:
> When enabling in ardour 0.9beta29 Display -> Show waveforms while
> recording I see a steady increase in memory occupation during recording
> (10 channels) 'till my ram is exhausted: ardour/jack are crashing. I run
> a patched 2.6.13-rc7 kernel. But:

i believe this was fixed in beta30.

> Now, I think, could it be, that ardour needs for the wave-forms display
> proportional to the recording memory in /dev/shm (which is limited to
> half the physical ram).

absolutely not. every waveform display object on the screen uses a cache
of pixel data that is twice the width of the X display, or the length of
the audio region, whichever is smaller. the requirements for waveform
display do not increase linearly with duration.

> be, that jack should not be compiled to run with tmpfs, but instead
> should be compiled to run with a tmp file system on ext2. ext2 I have
> already for the wave data.

you are missing the entire reason for using tmpfs. it has nothing to do
with wave display or audio. JACK uses FIFO's to wake up clients; it does
so by writing single bytes to these FIFO's. if they are placed in a
regular filesystem, this requires going through the code for (say) ext2
filesystem access, which has locks and other nasty non-RT friendly
components. using tmpfs means that i/o to FIFOs like this does not cause
xruns.





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