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

[RW <kvm@tauceti.net>]

I've read the article a few days ago and it was interesting.
As I upgraded vom 2.6.29 to 2.6.30 (Gentoo) I also saw a dramatic
increase disk and filesystem performance. But then I realized
that the default mode for ext3 changed to "data=writeback".
So I changed that back to "data=ordered" and performance was
as it was with 2.6.29.

I think ext3 with "data=writeback" in a KVM and KVM started
with "if=virtio,cache=none" is a little bit crazy. I don't know
if this is the case with current Ubuntu Alpha but it looks
like so.

Regards,
Robert

> 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.
>
> en comparing SQLite under the host against the guest OS,  there is an
> der of magnitude _IMPROVEMENT_ in the measured performance  of the guest.
>
> I am expecting that the host is doing synchronous IO operations but
> somewhere in the stack the calls are ultimately being made asynchronous
> or at the very least batched for writing.
>
> On the surface, this represents a data integrity issue and  I am
> interested in the KVM communities thoughts on this behaviour.  Is it
> expected? Is it acceptable?  Is it safe?