Re: [PATCH v4 0/8] Introduce the microvm machine type

[David Hildenbrand]

On 25.09.19 10:26, Paolo Bonzini wrote:
> On 25/09/19 10:10, Sergio Lopez wrote:
>> That would be great. I'm also looking forward for virtio-mem (and an
>> hypothetical virtio-cpu) to eventually gain hotplug capabilities in
>> microvm.
> 
> I disagree with this.  virtio is not a silver bullet (and in fact
> perhaps it's just me but I've never understood the advantages of
> virtio-mem over anything else).

Sorry, I had to lol about "virtio-mem over anything else". No, not
starting a discussion.

> 
> If you want to add hotplug to microvm, you can reuse the existing code
> for CPU and memory hotplug controllers, and write drivers for them in
> Linux's drivers/platform.  The drivers would basically do what the ACPI
> AML tells the interpreter to do.
> 
> There is no reason to add the complexity of virtio to something as
> low-level and deadlock-prone as CPU hotplug.

I do agree in respect of CPU hotplug complexity (especially accross
architectures), but thinking "outside of the wonderful x86 world", other
architectures impose limitations (e.g., no cpu unplug on s390x - at
least for now) that make something like this very interesting. But yeah,
I already expressed somewhere else my feelings about CPU hotplug.

I consider virtio the silver bullet whenever we want a mature
paravirtualized interface across architectures. And you can tell that
I'm not the only one by the huge amount of virtio device people are
crafting right now.

-- 

Thanks,

David / dhildenb