[PlanetCCRMA] The results of my not so great tests

fonse006 fonse006@csusm.edu
Wed Dec 29 15:47:02 2004

     This email is essentially just a report on my experiences with the latest 
kernels the kernels that tried to test were 2.6.9smp, 2.6.10smp,  2.6.10, 
2.6.9-2.2.rdt.rhfc2.ccrma, 2.6.9-2.2.rdt.rhfc2.ccrmasmp, and the old 
     The way that I tested them was I took a cue from someone else on this 
list, I forget who it was, used jack and ardour to record 4 audio tracks each 
with four plugins.  Three of the tracks were just background noise, but the 
fourth was a midi track that I used to vary the cpu load.  What I will report 
is the lowest latency that I was able to achieve under each kernel with the 
base tracks running in ardour and myself not raising the cpu load and I will 
report how high I had to raise the cpu load in order to get xruns.
stock 2.6.9smp-
latency- 5.33 msec,  xrun-cpuload-about- 65-70%
was not tested as jack crashed 4 times in a row within 30 seconds of opening
unless I turned realtime off, it did not matter whether I used jackd or 
latency- 0.667 msec, xrun-cpuload- 55-60%
latency- 2.67 msec,   xrun-cpuload- 90-95%
latency- 2.67 msec,  xrun-cpuload- 85%
latency- 10.7 msec,  xrun-cpuload- 65%

     I think that the easiest thing to say is that things are looking up for 
the 2.6 kernel version.  Currently I think that the most usable system is 
2.6.10 (that is if you are willing to run all of your audio software as root, 
which is not a good idea as a bad bug could bring your system to its knees), 
but the reatime-preempt patch delivers one quarter the latency, but there does 
seem to be some overhead involved in using the realtime-preempt patch as the 
base level cpuload for the realtime preempt patch was much higher than the 
rest (quite a bit more that I would expect from just transferring samples 4 
times as often. Also at least on my system the something in that kernel makes 
the system a lot less stable.  Ardour crashed like 3 times while I was doing 
the test, but not at all with any of the other kernels.  For all I know though 
this could be a problem with ardour.  Anyway, I think that is all that I had 
to say besides that these were very bad tests.  They are not in anyway 
scientifically valid.  I only did one test with each kernel and did not test 
more than one latency level with each kernel.  Those are just the two problems 
with my tests that come to mind right of the top of my head.  Results may