RE: 2.6.33-7-rt30 and 2.6.38 comparison

Victor henri
2011-03-27T13:21:21Z

Hello Jordan

>
> Hi Victor,
>
> > Same results (very few X-runs, if any) with :
> >
> > - on one hand, on an Asus laptop with a Core i3 : latency 2.3 msec
> > with the 2.6.33.7.2-rt kernel and 23 msec with a 2.6.37 preempt kernel;
>
> 23msec with 2.6.37 preemptive kernel is terrible. Not one of my
> machines would perform that badly (and most use 2.6.37.3). Some are
> also considerably older (like 5years older) than your asus laptop..
>
> > - on the other hand, on a Lenovo Thinkpad Core i5 : latency 2.3 msec
> > with the 2.6.33.7.2-rt kernel and 2.3 msec (yes the same) with a 2.6.37
> > preempt kernel !!
>
> that's not surprising, that is what i would expect to see. 2.6.33-rt
> is getting quite dated, and old. For industrial / embedded
> applications it might be the only option but for Linux audio / video
> editing, there are preemptive kernels that work very well.
>
> > Of course the Lenovo Thinkpad is a very good laptop, but how come that there is such a big difference?
>
> someone can probably answer this better, but i think it comes down to
> hardware / software design / implementation - some PCs work better
> because of the quality of parts, the software and how well they
> integrate.
>
> *** ....and how well-supported each component is under Linux. ***
>
> > So, I have observed the same quality of performance as Madovsky but not
> > on every machine I've used... I don't have a clue why....
>
> I also have observed the same thing. i actually only use RT on 1
> computer right now. On the Rest of my machines, 2.6.37.3-zen (PREEMPT,
> BFS and BFQ v2.0 + optimizations) works wonders.
> In every use i have 2.6.37 is better ( i am a pro-audio person ).

Could you briefly summarize why use zen-kernel instead of vanilla? As
far as I understand, the zen-kernel brings features that may not (yet)
be available on vanilla kernel, (such as those scheduler BFS and BFQ?) Could please say wich optimization is needed for the best performances? I'd like to give it a try actually. Or is there a place where I can find all these recommendations; I'm talking about the special features that you can find specifically in a zen-kernel, and that can help further for lower latency for music performance.

On the other hand, I've checked the www.zen-kernel.org website; the most recent kernel patch seem to be for 2.6.36 kernel; where did you find a 2.6.37 zen kernel?

>
> I will say between 2.6.33 and 2.6.38 they have been many MANY changes,
> so i am not surprised that 2.6.38 performs as well as 2.6.33-rt 9or
> even just close). 2.6.38 (i believe) is the First kernel to have BKL
> (Big kernel Lock) completely removed ....and also CFS (completely fair
> scheduler) have changed quite a bit (since .33) and has been more
> optimized. those 2 factors alone, should reduce latency. Coupled with
> other fixes and changes in the kernel - should explain these kinds of
> observations.
>
> just my 2 cents
>
> jordan
> --

Victor