[libvirt] PATCH: Disable QEMU drive caching

[Daniel P. Berrange]

On Wed, Oct 08, 2008 at 10:51:16AM -0500, Anthony Liguori wrote:
> A great deal of virtualization users are doing some form of homogeneous 
> consolidation.  If they have a good set of management tools or 
> sophisticated storage, then their guests will be sharing base images or 
> something like that.  Caching in the host will result in major 
> performance improvements because otherwise, the same data will be 
> fetched multiple times.

NB, this has no impact on caching of backing files - QEMU masks out
the O_DIRECT flag when opening the backing file - so in a shared
master image scenario, all reads for the shared file will still be 
cached, only write5Cs to the cow file are impacted.

Daniel
-- 
|: Red Hat, Engineering, London   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|