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 ([EMAIL PROTECTED]) (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 ([EMAIL PROTECTED]) (gcc version 2.96 20000731 (Red Hat Linux 7.3 2.96-112)) #1 Tue Oct 8 13:33:14 EDT 2002 kjetism@olivier ~ $ --
