Host is MacBook Pro 2.4GHz, 4GB RAM, OSX 10.5.4. Guests get 768 MB RAM. When Guest is idle, CPU usage on host is stable ~10%, which is very nice.
But using the virtual sound card significantly affects host CPU load.
32-bit Win 7 uses the driver found with Windows Update.
64-bit Win 7 uses the latest March 2009 Realtek x64 AC97 driver (6303_Vista_Win7_PG537.zip).
This is what I've found on both 64-bit and 32-bit Win 7 RC:
1. When playing audio on Guest, CPU usage on Host rises significantly. 32-bit Win 7 driver runs Host CPU at around 75%, 64-bit Realtek driver runs Host CPU even worse, at around 85-90%.
Note that Process Explorer running minimized in the system tray shows that CPU usage on Guest is pretty much idle, as it should be. Screenshots are taken of 32-bit Windows 7 machine.
2. When audio is stopped, but media player stays running, CPU cycles are still being eaten although a bit less - around ~60% now. Guest is idle. I guess virtualization engine still needs to work hard when the sound card handle is open in Windows? Maybe a place for optimization?
3. Closing media player immediately releases CPU on Host.
This might not even be a problem, because I don't know - maybe sound card really is that CPU expensive to virtualize and there is no cure. I am really hoping this can be improved though, it would be really nice to run Windows sound apps in a quiet laptop! Any thoughts?