Re: [GIT PULL] AlacrityVM guest drivers for 2.6.33

Avi Kivity
2009-12-23T10:22:29Z

On 12/23/2009 12:13 PM, Andi Kleen wrote:
>> i.e. it has all the makings of a stupid, avoidable, permanent fork. The thing
>>
> Nearly. There was no equivalent of a kernel based virtual driver host
> before.
>

These are guest drivers. We have virtio drivers, and Xen drivers (which
are Xen-specific).

>> - Are a pure software concept and any compatibility mismatch is
>> self-inflicted. The patches are in fact breaking the ABI to KVM
>>
> In practice, especially considering older kernel releases, VMs
> behave like hardware, with all its quirks, compatibility requirements,
> sometimes not fully understood, etc.
>

There was no attempt by Gregory to improve virtio-net.

>> It's a bit as if someone found a performance problem with sys_open() and came
>> up with sys_open_v2() and claimed that he wants to work with the VFS
>> developers while not really doing so but advances sys_open_v2() all the time.
>>
> AFAIK Gregory tried for several months to work with the KVM maintainers,
> but failed at their NIH filter.
>

It was the backwards compatibility, live migration, unneeded complexity,
and scalability filters from where I sit. vbus fails on all four.

>> The main difference is that Gregory claims that improved performance is not
>> possible within the existing KVM framework, while the KVM developers disagree.
>> The good news is that this is a hard, testable fact.
>>
> Yes clearly the onus at this point is on the vhost-net developers/
> "pci is all that is ever needed for PV" proponents to show similar numbers
> with their current code.
>
> If they can show the same performance there's really no need for
> the alacrityvm model (or at least I haven't seen a convincing reason
> other than performance so far to have a separate model)
>

Anthony posted this:

http://www.redhat.com/f/pdf/summit/cwright_11_open_source_virt.pdf

See slide 32. This is without vhost-net.

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