linux-kernel - Re: [QUERY] lguest64

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Date:	Wed, 31 Jul 2013 17:32:36 +0300
From:	Mike Rapoport <mike.rapoport@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [QUERY] lguest64

On Wed, Jul 31, 2013 at 4:19 PM, H. Peter Anvin <hpa@...or.com> 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,
Mike.
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