Re: sync guest calls made async on host - SQLite performance

[Anthony Liguori <anthony@codemonkey.ws>]

Matthew Tippett wrote:
> Hi,
>
> I would like to call attention to the SQLite performance under KVM in 
> the current Ubuntu Alpha.
>
> http://www.phoronix.com/scan.php?page=article&item=linux_2631_kvm&num=3
>
> SQLite's benchmark as part of the Phoronix Test Suite is typically IO 
> limited and is affected by both disk and filesystem performance.

Gotta love Phoronix's transparent methodology...

Ubuntu's Karmic release has _not_ been released yet.  For this 
particular test, Phoronix was probably using an alpha drop before Ubuntu 
switched from kvm-84 to qemu-kvm-0.11.0.

Before 0.11.0, there were known issues with qcow2 and it was not 
recommended for use in production environments.  If you read the release 
notes for 0.10.0, we made this very clear.  Because of some performance 
problems, in 0.10.x we made cache=writeback the default for qcow2.  We 
document this pretty thoroughly.  See 
http://www.qemu.org/qemu-doc.html#SEC10  Some other distros that shipped 
0.10.x made cache=none the default in order to ensure data integrity (at 
the cost of performance).

For 0.11.0, Kevin Wolf has fixed the performance/reliability issues in 
qcow2 and we now set cache=writethrough for qcow2 by default.

And FWIW, Karmic has been on the 0.11.0 tree now for at least a month.

Regards,

Anthony Liguori