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

[Avi Kivity <avi@redhat.com>]

On 09/23/2009 06:58 PM, 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.
>
> When comparing SQLite under the host against the guest OS,  there is 
> an order 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?

qemu defaults to write-through caching, so there is no data integrity 
concern.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.