On 05/17/2010 03:31 PM, Eric Blake wrote:
[adding Matthias on cc]
Reviving an old thread, as it is something I plan on working in the near future.
On 05/17/2010 03:07 PM, Chris Lalancette wrote:
On 05/12/2010 11:26 PM, Eric Blake wrote:
From: Matthias Dahl <mdvirt@designassembly.de>
qemu allows the user to choose what io storage api should be used, either the default (threads) or native (linux aio) which in the latter case can result in better performance.
The implementation looks perfectly reasonable. I'm just concerned that the concept of what we are doing is too qemu specific, though. Basically, I think what we are trying to model here is the concept of an I/O backend implementation, correct? Should we maybe change this to be "<iobackend type='%s'/>", and then have available enums like:
aiothreads aionative ...
That way, for other hypervisors that do something different (like VirtualBox, which just has AIO on/off), we can have additional enums to describe their behavior. Even further, if a given hypervisor wanted to do something like "Direct I/O" for the I/O backend (as an example), we could also use this element to specify that. What do you think?
Indeed, having a more-generic attribute "type", where only a subset of known enum values are appropriate per a given hypervisor, makes sense to me.
I'm thinking that the following XML changes make the most sense for this (note that the choice of aio mode is per-disk), where the change is the addition of the new <iobackend> element: <domain ...> <devices> <disk type='block' device='disk'> <driver name='qemu' type='qcow2' cache='none'/> <source dev='...'/> <target dev='hda' bus='ide'/> <iobackend type='aiothreads'/> </disk> </devices> </domain> If <iobackend> is missing, it is the same as type='default'; type can be 'default' (whatever qemu prefers, which may differ over qemu versions), 'aiothreads' (use ,aio=threads in qemu -drive argument), or 'aionative' (use ,aio=native in qemu -drive argument); where we can add other types later if needed. Does this deserve a new <iobackend> element, or should it merely be a new optional attribute of the existing <driver> element, as in: <driver name='qemu' type='qcow2' cache='none' iobackend='aiothreads'/> -- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org