I've been trying to enable sound for the linux-virtual kernel as I want to run an ultra slim Ubuntu server under VirtualBox but need audio. The resource usage difference between virtual and generic/server is surprisingly large, with the virtual kernel system using 80Mb less RAM after a clean boot (130Mb vs 210Mb), and I really want to squeeze every clock cycle and available byte I can out of the system. Besides, the virtual kernel has some additional optimisations enabled specifically for virtual machines (or so I am told).

Now I have compiled my own kernel a few times in the past, for example to include the Intel-PHC module (for improved power management on Thinkpads), so the concept is not entirely alien to me, but I've run into a strange problem which I'm hoping someone can help explain: When I do a diff between the config files for Linux-generic and Linux-virtual there are precious few differences, and certainly none which pertain to sound support; there are really only five or six lines which differ, and they're mainly to do with i/o timing, sleep state and priorities. What gives? I expected the differences to be extensive, and that I would be able to identify the options that enabled audio by looking at them, but my problem doesn't seem to be related to the config file at all (yes, I know about the sound drivers section - it is identical between the two kernel configs). Am I looking in the wrong place?

Many thanks!