Subject: Re: [Jackit-devel] Re: [PD-announce] Re: [linux-audio-dev] ANN: k_jack v0.0.0.5 and Mammut v0.15
From: Kjetil S. Matheussen (k.s.matheussen@notam02.no)
Date: Fri Jan 24 2003 - 18:36:30 EET
On Fri, 24 Jan 2003, Paul Davis wrote:
> >Hmm, this is quite interesting. With a period size of 64 frames,
> >you'd get quite a lot of context switches with jackd. Kjetil, does
> >your ipc-lib make the context switches this often?
> >
> >Another interesting this is how this high interrupt frequency affects
> >scheduling of (non-root) processes. I'd guess it could have a notable
> >impact on reliability... have to try this later today with jackd.
>
> i have been unable to reliably run jackd with a period size of 64
> frames on my dual CPU system. you may recall that i spent considerable
> time trying to track down what was preventing it from happening, to no
> avail. something in the kernel appears to prevent reliable scheduling
> at this level. that is, jackd is not reliably woken by the kernel when
> the audio interface interrupt arrives, or rather, its not reliably
> woken in time to properly service the interrupt. and if not that, then
> the kernel fails to reliably and promptly schedule the other
> clients. with only 2 periods per buffer, these scheduling errors are
> fatal. it will be interesting to see how 2.5 performs in this regard.
>
> pd (with the configuration kjetil has shown) would be unaffected by
> this unless it affected 27 periods in a row, which is rather
> unlikely.
>
Let me just say that I have just tested to see if k_jack could handle
lower latencies than 39msec running one freqtweak. And indeed it does. 9
msecs seems to work fine (no overruns), even when compiling QT3.1.1 in the
background. 4 msecs works too, but overruns happens when doing X things.
The machine this was tested on is an Asus a7n266-vm with xp2100 processor,
wd 8mb cache ide HD, 512 mb memory, inboard geforce2 gfx card and delta 44
soundcard.
kjetism@hensten ~ $ more /proc/version
Linux version 2.4.18-18.7.x (bhcompile@bugs.devel.redhat.com) (gcc version
2.96 20000731 (Red Hat Linux 7.3 2.96-112)) #1 Wed Nov 13 20:29:30 EST
2002
On the other hand, 39msec does not work very fine on an other machine.
It is a 733mzh piii with asus cucl2 (or something) mainboard, 256 mb
memory, matrox g550 gfx card, samsung ide HD and delta 44 soundcard.
I _suspect_ its the GFX card (or driver) thats causing this.
kjetism@olivier ~ $ more /proc/version
Linux version 2.4.18-17.7.x (bhcompile@daffy.perf.redhat.com) (gcc version
2.96 20000731 (Red Hat Linux 7.3 2.96-112)) #1 Tue Oct 8 13:33:14 EDT 2002
kjetism@olivier ~ $
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