Tuesday 23 May 2006 19:13, Lee Revell: > On Wed, 2006-05-24 at 10:28 +0200, Wolfgang Woehl wrote: > > Hi, I want to try what Lee mentioned a couple of times recently: Low > > latency audio performance with 2.6 mainline -- no mingo-patch, no rt-lsm > > (athlon xp 2600+, asus a7v8x-x, hdsp. On a 2.4.26 with lck patches this > > system has good lowlat performance, solid jackd with -p 64 -n 2, so the > > hardware should be ok. Ah well, looong dropouts on deep reiserfs walks > > that never show up in jackd's messages but that's hopefully another > > story). > > > > Got 2.6.16.16 from kernel.org. If I understood Lee right I could expect a > > jackd with -p 64 -n 2 to work just fine but it doesn't. Loads of xruns. > > What am I missing? What can I do to find out? > > -p 64 -n 2 is pushing the envelope of what the mainline kernel can do. > 128 or 256 should be solid. It will depend on the hardware and driver > set. Run as root I get no xruns with a jackd -R -d alsa -p 64 -n2 (2.6.16.16-vanilla), with one of my average sessions (~8 tracks with plugins) the average jackd message is like load = 17.4066 max usecs: 207.000, spare = 1244.000 (Only with a 70 tracks ardour session there are occasionals but the disk settings in ardour.rc seem to make a difference, they shouldn't I guess.) This is great. Vanilla for me from now on. > > Reiserfs is a poor choice of filesystem for low latency. > > Also make sure you are in realtime mode - depending on the distro, the > realtime LSM may still be required. I guess you are using the PAM > method to enable non-root realtime? I hadn't done my homework and wasn't aware of the privilege separation between root and users. So I had tried without any of the 3 possible mechanisms (pam, set_rlimits, rt-lsm?). And the way things are that doesn't work, ok. Thanks for the hint, Lee. Damn, it doesn't make sense to me. If I can configure the kernel to be or not to be preemptible then what is the separation good for? Isn't overhead because of preemption the only price tag? -- Wolfgang
