Measured on a VM with two disks, a CD-ROM and a NIC: 70 libvirt calls per
page, now 43. Within the page's cached_reads block the VM's state, the
host's info and domain capabilities, and each disk path's volume are read
once; the running and the persistent disk lists share a path's volume.
The ISO list takes the active pools in one call instead of looking each up
by name; it still refreshes them, so an image copied in by hand shows up.
The opt-in DRBD status waits at most 10 s for the compute's ssh, then
leaves the status unknown instead of holding the page.
The VM page's getters read the domain XML on their own: one load made
86 libvirt calls for a real VM, 29 of them for the same three XML
documents (live, live with secrets, persistent) and 6 for the host
capabilities. Each call is a round trip to the host.
wvmInstance.cached_reads() is a block in which _XMLDesc (per flags
value) and get_cap_xml are read from libvirt once; it ends with the
block, even on an error, does not nest, and _defineXML drops it.
Outside a block every read goes to libvirt as before. Only the VM page
view, which does not change the VM, uses it, around its rendering.
Views that change the VM keep reading fresh XML: most changes (devices,
QoS, memory) do not go through _defineXML, and several views read,
change and define more than once in one request.
Measured on the test host: 86 -> 55 calls (XMLDesc 29 -> 3,
getCapabilities 6 -> 1) for one VM, 82 -> 54 for another; the page took
0.23-0.25 s before, 0.14-0.15 s after. The HTML of both pages is
identical before and after (CSRF tokens aside). A test renders the page
on libvirt's test driver through the real getters: 25 XML reads before,
one per kind now.
