stats : active memory / disk latency

Two stats that VMWare offers that I can't seem to find in libvirt is "active" memory and disk latency. Any idea how I could extract these stats? libvirt offers memory stats such as maximum, current, unused, usable, etc. but these are all 100% or 0% of what the VM has available. Looking for an "active" value. /proc/memstat has similar stats within a Linux VM but need to get from libvirt. Disk latency is also sometimes critical information. Thanks, -- Peter Quiring