why did Ubuntu turn off kernel preemption in Edgy?

[Kevin Perros]

> First of all, for all the ones experiencing sound hickups under
> I/O-load; you issue most likely have nothing or at least very little
> to do with either preempt or the timer interrupt. Back in 2.4 very
> modest hardware already could perform sound-playback and disk-i/o
> simultaneously without problems. In fact, at the time (99-ish), that
> was one of Linux big strengths compared to both Mac and Windows. If
> you're having problems with I/O-interference your most likely source
> is the driver. For some SATA-controllers I know 2.6.17 had issues, I
> experienced them personally, and 2.6.19 distributed right now with
> Feisty helped, at least myself. Possibly, the io-scheduler can help
> you a little too, with a buggy I/O-driver, it's my experience that the
> noop-scheduler often performs best. (Believe it or not) And remember,
> do some kind of FS-bench, rather than hdparm if you want to bench it,
> and remember to flush you I/O-cache.

Whatever the reason, preempt often solves the problem. So I believe it 
should be activated.

Before the use of this patch, sound playing was often glitchy, with 
hardware very well documented and largely spread (I remember having this 
problem with ens1370 and ens1371). Since the 2.6 kernel series, there 
are two kind of distribution : those who glitches and those who do not 
with the same hardware.

Whatever the fix, sound must not glitch under normal load (i.e. heavy 
cpu and i/o load with normal priority apps). If the fix consists in 
patching every driver, it is a good solution. If time lacks to fix every 
driver, the preempt patch must be used.

PS: I now understand why the sound glicthes on my Ubunutu