FreeBSD 6.2-PRE: Jumping box. Worse performance

[O. Hartmann]

Compiling FreeBSD's world with make -j2 was never a problem while playing sound or doing other work on screen - but this seems to be a big problem now, even when SCHED_4BSD is used!

While compiling world mouse stops and jumps, sound gets distorted. I recognise thsi behaviour also when box is doing minor HD access: mouse pointer stops, keyboard input gets stuck, sound stops playing, window operations (opening/closing) seems to freeze. This got even worse whithin the last two weeks (date when it starts getting this worse unknown).
This phenomenon occurs on both i386 and amd64 but is much worse on amd64. On AMD64 very short and small HD activities seems to trigger this 'jumping' and stopping.

Both boxes are singel core CPUs, AMD64 is a Athlon 3500+, i386 is a HTT enabled P4 at 3.0 GHz.

I do not get any error or system fault, simply this jumping and freezing.

On both systems PREEMPTION is enabled in the kernel, but the problem also occurs without this option.

Any ideas, suggestion, maybe explanations?

Regards,
Oliver