[uml-user] slow ubd performance

[Riccardo M. <ric...@gm...>]

Hi *,

the file-backed `ubd` devices in my UML instances are terribly slow,
and generate a lot of "iowait" load on the host.  It looks like as if
filesystems mounted from `ubd` devices were using the `sync` option.

This happens with kernels downloaded from uml.devloop.org.uk, as well
with kernels that I compiled myself (but using basically the same
config as the devloop ones); I tried 2.6.38.x and 2.6.39.x (for some
random values of "x").

This does *not* happen with Debian/Ubuntu's kernel 2.6.32.5, which
unfortunately exhibit a filesystem corruption bug.

The host is in any case Ubuntu "natty", running 2.6.39-3-generic.

Is this expected?

Thanks,
Riccardo