* Anthony Liguori (anthony@xxxxxxxxxxxxx) wrote: > On 12/02/2010 03:07 PM, Chris Wright wrote: > >Like non-trapping hlt, that too will guarantee that the guest is preempted > >by timeslice exhaustion (and is simpler than non-trapping hlt). So it > >may well be the simplest for the case where we are perfectly committed > >(i.e. the vcpu fractional core count totals the pcpu count). But once > >we are undercommitted we still need some extra logic to handle the hard > >cap and something to kick the running guest off the cpu and suck up the > >extra cycles in a power conserving way. > > I'm not entirely sure TBH. > > If you think of a cloud's per-VCPU capacity in terms of Compute > Units, having a model where a VCPU maps to 1-3 units depending on > total load is potentially interesting particularly if the VCPU's > capacity only changes in discrete amounts, that the expected > capacity is communicated to the guest, and that the capacity only > changes periodically. OK, let's say a single PCPU == 12 Compute Units. If the guest is the first to migrate to a newly added unused host, and we are using either non-trapping hlt or Marcelo's non-yielding trapping hlt, then that guest is going to get more CPU than it expected unless there is some throttling mechanism. Specifically, it will get 12CU instead of 1-3CU. Do you agree with that? thanks, -chris -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
