Re: I/O performance in hvm domU

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Tue, Sep 01, 2009 at 10:21:36PM +0200, Linus Nordberg wrote:
> Hi,
> 
> I'm running FreeBSD (6.3) in a hvm domain on NetBSD (5.0.1) and suffer
> from pretty bad I/O performance.  I realize that disk I/O should be
> punished for going through qemu but would like to hear if my figures
> make sense.
> 
> I've been running bonnie on both the domU and the dom0, using a file
> system on the same disk device on the dom0 as the one on which the files
> backing the domU disks resides.  The amount of data used for testing has
> been chosen to be equal to the amount of RAM available to the domains,
> 2GB and 256MB for the domU and the dom0 respectively.
> 
> Write performance in domU is 11% and 9% of that for dom0 for char and
> block writes, respectively.  For disk reads these figures are 36% and
> 44% and for random seek performance it's 23%.  The "rewrite" figure is
> actually slightly better in domU than dom0 (103%).
> 
> Any thoughts on this?  Does it seem reasonable to you?

For a HVM guest with emulated I/O it looks reasonable to me. 
This matches more or less what I've seen with a linux HVM guest ...

-- 
Manuel Bouyer, LIP6, Universite Paris VI.           
Manuel.Bouyer%lip6.fr@localhost
     NetBSD: 26 ans d'experience feront toujours la difference
--