Re: Question about KVM on Big.Little SoC

[Marc Zyngier <marc.zyngier@arm.com>]

Peng,

On 06/09/16 09:00, Peng Fan wrote:
> Hi Andre,
> 
> I came across your patch which try to fix kvm on big.little.
> https://lists.cs.columbia.edu/pipermail/kvmarm/2013-April/003989.html
> 
> I am trying KVM on a big.little SoC with 4 A53 and 2 A72.
> I wonder whether kvm supports running on big.little SoC now?
> 
> I am checking arch/{arm,arm64}/kvm code, but I think you may give a quick answer.
> 
> And If kvm supports running on big.Little SoC, is it ok for me to pass "-cpu host"
> to qemu? Can guest vcpu be scheduled freely on big and little SoCs?
> 
> Would you please kindly give me some clues about where is the piece code to handle
> kvm on big.little?

The current situation is that:

- Yes, KVM works on big-little systems (it always had)
- The only useful option you can pass to qemu is "-cpu host"
- There is no guarantee that QEMU will even start, unless you constraint
its affinity to one single type of CPUs (use taskset).
- If you use taskset, there will be no scheduling between types of cores
- If you do not, scheduling will happen, but that's a fairly unsafe
thing to do (the guest doesn't know it is being migrated between CPUs
that may have different behaviours...).

Hope this helps,

	M.
-- 
Jazz is not dead. It just smells funny...