xen domu disk performance

[Blair Sadewitz <blair.sadewitz%gmail.com@localhost>]

Hello,

I'm sure this has been asked before, but I'm wondering what I can try
tuning to get better performance in a -current domu.

Specifically, I noticed: xbd0: WARNING: cache flush not supported by backend

and the existence of this: vfs.wapbl.flush_disk_cache

I get absolutely miserable performance doing something like untarring
a source tree.  If anyone wants more information, just ask.

I've seen discussions about it, but I don't want to put the cart
before the horse.  Anything I should try?

Thanks,

--Blair