[libvirt-users] [API reference] confused by CPU time term

Hi, everyone I'm writing a virtual machine monitor based on libvirt. As I read the api reference, I found I'm confused by some terms. 1, What is cumulative I/O wait CPU time? API reference says that VIR_NODE_CPU_STATS_IOWAIT indicate cumulative I/O wait CPU time. I'm confused by this time. As far as I know, when cpu meets IO wait situation, it will schedule another task, so, how this IO wait time is accounted? 2, How do I get VCPU runtime? In my mind, VIR_DOMAIN_CPU_STATS_CPUTIME indicates the physical cpu time consumed by the domain. Is there any API by which I can query virtual CPU running stats in one domain?