(Apparently I managed to screw up sending that, twice. Long weekend.)
Please consider adding the option of setting the "io" attribute when
attaching disks to guests. Under Red Hat (unsure if this is true under
vanilla libvirt), virt-install and virt-manager both default to
explicitly setting "io='native'" in the disk "driver" tag.
virsh,
however, does not and also does not provide an option to specify that
setting at all. As a result, disks use a different IO mechanism (the
default, "threads") when attached post-setup using virsh. Adding this
option allows users to keep disk performance consistent for disks
attached at install, and those attached afterward.