I have the same behavoir on my asus s5200n. When i loging to X session 
via xdm fvwm and his scripts starting much slowely that before.
The problem appear after i upgrade my 4.0 kernel from December build.


Sat, 20 Jan 2007 you wrote:

> Interactive performance on my Thinkpad T42 has become completely
> unacceptable.  Something else -- I have no idea what -- occasionally
> grabs the CPU.  Moving the mouse shows jerky cursor motion, I get
> doubled input characters, etc.  ps and top show that the machine is
> mostly idle, though xosview sometimes shows brief spurts of 100% busy.
> It isn't swapping (it's got 2G of RAM), the interrupt load doesn't seem
> high (about 1.4-1.6K/sec, with HZ set to 1000), etc.  

> Is anyone else seeing this?  Anything I should do to tune it?  Might
> the new scheduler code be part of it?

Alex