4-core server running multiple headless VirtualBox instances: slow?

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https://bbs.archlinux.org – Like title, I have a VM server that hosts about 15-ish VMs, and when about ~5 of them are running and I do something major on one of them (like compile software), the server gets excruciatingly slow.  The SSH console even takes ~15s to respond to keyboard input, for example.  How can I fix this?  Shouldn't the kernel's scheduler manage the individual processes of the VMs and prevent this? synthead https://bbs.archlinux.org/profile.php?id=6032 2012-10-03T20:49:20Z (HowTos)