winxp in qemu+kvm on ubuntu 10.04: extremely poor performance
As the title says, I'm using qemu and kvm to run some WinXP guests on an Ubuntu 10.04 host, and find the performance of the guests is horrible. Installation takes 3 hours, installing some simple patches through windows update takes an hour, installing .net framework takes an hour, unzipping and copying files is slow..
During installation and subsequent setup, the guest shows hardly any cpu / memory usage, in windows task manager as well as virt-manager, but I can hear the host's hard drives working in little bursts. vmstat puts the host's cpu at 60-80% idle 20-40% io wait, which I suppose is bad.
I have verified the kvm module is being loaded and used correctly.
I've tried changing from qcow2 to raw images, this helped speed up the installation but patching and software install is still horribly slow. I've read there are problems with acpi on WinXP guests so I turned it off (in virt-manager and in the guest OS - using the Standard PC HAL) but this made little difference if any.
The disk image files are on a journaled ext4 filesystem, I'm not sure that was a good idea?
On my other computer I have used XP guests on a Slackware host, also using kvm, (and also on a journaled filesystem) and performance was an order of magnitude better there, even with older hardware, so I feel it must be some misconfiguration in the ubuntu host OS or the way it handles the guests.
Any ideas as to what would cause such a massive slowdown?