Thanks Avi, I am still trying to reconcile the your statement with the potential data risks and the numbers observed. My read of your response is that the guest sees a consistent view - the data is commited to the virtual disk device. Does a synchronous write within the guest trigger a synchronous write of the virtual device within the host? I don't think offering SQLite users a 10 fold increase in performance with no data integrity risks just by using KVM is a sane proposition. Regards... Matthew On 9/24/09, Avi Kivity <avi@xxxxxxxxxx> wrote: > 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. > > -- Sent from my mobile device -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
