process load and swapping

I have been experiencing the following behavior on my alpha with many kernel versions (2.4 series, latest is 2.4.19 with Ingo's O(1) scheduler patch).

I'm running apache and zope, and when I load a zope page, the load jumps to ~12 and the computer starts skipping. That is, about once every 2s the music (xmms) stops for ~0.5s and then comes back. This repeats every 2s until zope is finished creating the page (which takes sometimes longer than a minute). When the computer "skips", not only does the music stop, but the mouse stops moving (i.e. I move it continuously and it pauses for 0.5s every 2s). This happens both at the console in X and on virtual terminals (ssh'ed from another computer). It's as if it's not servicing interrupts for 0.5s. Or does scheduling not occur when the kernel decides to load N pages from swap, no matter how large N is?

This is totally due to swap use. If I turn off all swap ('swapoff -a'), the response of zope is speedy. This behavior has happened with all kernel versions I have used, at least since 2.4.17.

So, any ideas? I know there have been arguments about the 'swappiness' of this kernel, but the load going to 12 and interrupts not being serviced is totally quantitative and totally repeatable...

Cheers,
-- Bob

Bob McElrath
Univ. of Wisconsin at Madison, Department of Physics

"The surest way to corrupt a youth is to instruct him to hold in higher esteem those who think alike than those who think differently."
-- Nietzsche