Re: [PATCH] kvm-vmx: add module parameter to avoid trapping HLT instructions (v2)

Anthony Liguori
2010-12-02T22:38:03Z

On 12/02/2010 03:07 PM, Chris Wright wrote:
>> But you agree this is no KVM business.
>>
> 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.

Regards,

Anthony Liguori

> thanks,
> -chris
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