1. The guest OS calls HYPERVISOR_block() (thus setting the BLOCKED flag) whenever it wants to yield the processor because it's waiting for an event. 2. This blocking can happen anytime -- including after the guest OS has been running for quite some time. Both correct! 3. All the "event_pending(prev)" check in __enter_scheduler() is for is to say "whoops, an event arrived in the time between when the guest OS blocked & right now, so I should clear the BLOCKED flag." This is true as well! This is so the domain can be rescheduled at the scheduler's earliest discretion (possibly immediately).

If these are true, then the original code was correct -- "prev->cpu_time" should be updated during any call to the __enter_scheduler() function, regardless of the state of the BLOCKED flag.

Which makes me wonder if something is seriously misbehaving to cause the weird CPU usage totals you're seeing -- like a yield()ed or block()ed domain improperly getting rescheduled immediately, or an improper modification of the prev->lastschd counter, or the "if (prev == next)" optimization [later in __enter_scheduler()] leaves out some crucial accounting, or...?