Re: [PATCH RFC 0/2] KVM: use RCU to allow dynamic kvm->vcpus array

[Paolo Bonzini]

On 17/08/2017 09:36, Cornelia Huck wrote:
>> What if we just sent a "vcpu move" request to all vcpus with the new 
>> pointer after it moved? That way the vcpu thread itself would be 
>> responsible for the migration to the new memory region. Only if all 
>> vcpus successfully moved, keep rolling (and allow foreign get_vcpu again).
>>
>> That way we should be basically lock-less and scale well. For additional 
>> icing, feel free to increase the vcpu array x2 every time it grows to 
>> not run into the slow path too often.
> 
> I'd prefer the rcu approach: This is a mechanism already understood
> well, no need to come up with a new one that will likely have its own
> share of problems.

What Alex is proposing _is_ RCU, except with a homegrown
synchronize_rcu.  Using kvm->srcu seems to be the best of both worlds.

Paolo