linux-kernel - Re: [QUERY] lguest64

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Message-ID: <51F90EE0.4070108@zytor.com>
Date:	Wed, 31 Jul 2013 06:19:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Rapoport <mike.rapoport@...il.com>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [QUERY] lguest64

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.

>>>> 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.

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

	-hpa


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