pvUSB backend performance

[Juergen Gross <jgross@suse.com>]

Hi,

my qemu integrated pvUSB backend is now running stable enough to do
some basic performance measurements. I've passed a memory-stick with
about 90MB of data on it to a pv-domU. Then I read all the data on
it with tar and looked how long this would take (elapsed time):

in dom0:                     5.2s
in domU with kernel backend: 6.1s
in domU with qemu backend:   8.2s

So the qemu backend is about 30% slower than the kernel backend. Is
this acceptable?

BTW: I managed not to have to copy the I/O-data in the backend, it is
just mapped into user space and then given to the USB framework of qemu.
I think it will be copied there, but changing this will require a lot
of work...


Juergen