Hello,
I have been playing with kernel 2.5/2.6 for around 6 months now. I was quite pleased with 2.5.65 to see that the soft real-time behaviour was much better than 2.4.x. Since then I tried most of the 2.5/2.6 versions. But recently someone warned me about some degradations with 2.6.0-test6. To show the degradation since 2.5.66 I have run a simple test program on most of the versions. This simple program is measuring the time it takes to a process to be woken up after a call to nanosleep.
As the results are plots, please visit this small website for more information : http://perso.wanadoo.fr/kayakgabon/linux
I'm ready to perform more tests or provide more information if necessary.