ppc32: Weird process scheduling behaviour with 2.6.24-rc

[Benjamin Herrenschmidt]

On Fri, 2008-01-25 at 18:03 +1100, Benjamin Herrenschmidt wrote:
> On Fri, 2008-01-25 at 17:54 +1100, Benjamin Herrenschmidt wrote:
> > 
> > Here, I do the test of running 4 times the repro-case provided by Michel
> > with nice 19 and a dd eating CPU with nice 0.
> > 
> > Without this option, I get the dd at 100% and the nice 19 shells down
> > below it with whatever is left of the CPUs.
> > 
> > With this option, dd gets about 50% of one CPU and the niced processes
> > still get most of the time.
> 
> FYI. This is a 4 way G5 (ppc64)

I also tested responsiveness of X running with or without that option
and with niced CPU eaters in the background (still 4 of them, one per
CPU), and I can confirm Michel observations, it gets very sluggish
(maybe not -as- bad as his but still pretty annoying) with the fair
group scheduler enabled.

Here, X is running with nice=0

Ben.