Re: [QUERY] lguest64

From: Mike Rapoport
Date: Wed Jul 31 2013 - 10:32:51 EST

On Wed, Jul 31, 2013 at 4:19 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 07/31/2013 06:07 AM, Mike Rapoport wrote:
>>> "We can add a pvops user and that won't change the number of pvops
>>> users" What?!
>> We modify existing pvops user, IMHO. lguest is existing pvops user and
>> my idea was to extend it, rather than add lguest64 alongside lguest32.
> That is nothing but creative accounting, sorry.

If you count Xen PV 32 and 64 as two pvops users than indeed so :)

>>>>> Yes, the subset of x86-64 machines for which there isn't hardware
>>>>> virtualization support is pretty uninteresting.
>>>> There are plenty virtual machines in EC2, Rackspace, HP and other
>>>> clouds that do not have hardware virtualization. I believe that
>>>> running a hypervisor on them may be pretty interesting.
>>> The big problem with pvops is that they are a permanent tax on future
>>> development -- a classic case of "the hooks problem." As such it is
>>> important that there be a real, significant, use case with enough users
>>> to make the pain worthwhile. With Xen looking at sunsetting PV support
>>> with a long horizon, it might currently be possible to remove pvops some
>>> time in the early 2020s or so timeframe. Introducing and promoting a
>>> new user now would definitely make that impossible.
>> I surely cannot predict how many users there will be for nested
>> virtualization in public cloud from now till the point when public
>> cloud providers will allow usage of hardware for that purpose.
>> Nevertheless, I believe that nested virtualization in public clouds is
>> a real use case which will have real users.
> Then that will show... however, whether or not lguest64 will be used for
> that purpose is anyone's guess. I suspect personally that people will
> use the already-deployed Xen PV for that purpose and it will stretch the
> lifespan of that technology.

Well, nesting Xen PV in a cloud VM, even fully-virtualied, seems to me
significantly more complicated than nesting an lguest.

> Now, nested PV is an even uglier case, and at least some public clouds
> are using PV at the base layer.

Unfortunately, majority of public cloud VMs are PV. And, indeed,
nested PV is not nice...

> -hpa

Sincerely yours,
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