[Kata-hypervisor] Link to the Hypervisor Prototype

Anthony Liguori aliguori at amazon.com
Wed Jun 6 23:14:14 UTC 2018


"Jessie Frazelle (TUPPERWARE)" <jessfraz at microsoft.com> writes:

> Sorry outlook cut off the first line... windows...
>
> so rust :D

I was able to join the prep call at least and I raised this during that
discussion.  I'm not sure what problem this group is trying to tackle.

What was brought up on the call is a "cloud VMM" as an alternative to
QEMU but I don't really agree with that premise.  For the problem space
that QEMU tackles, it's hard to do better than it does and it tackles a
huge space.

Cloud is an extremely ambiguous term too.  In another part of this
thread, qcow2 was mentioned as a target which I don't think at all is
something that is interesting if you are an infrastructure provider.

There's lot of stuff that I am interested in (particularly around super
fast start up time and super low overhead to get high density) but
that's only possible to achieve if you constrain the problem space
tremendously.

Regards,

Anthony Liguori

>
> ________________________________________
> From: Jessie Frazelle (TUPPERWARE) <jessfraz at microsoft.com>
> Sent: Wednesday, June 6, 2018 6:37 PM
> To: Anthony Liguori; Ernst, Eric; Sasha Levin; Manohar Castelino
> Cc: kata-hypervisor at lists.katacontainers.io
> Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype
>
> Rust?
>
> What would you do?
>
> ________________________________________
> From: Anthony Liguori <aliguori at amazon.com>
> Sent: Wednesday, June 6, 2018 6:36 PM
> To: Jessie Frazelle (TUPPERWARE); Ernst, Eric; Sasha Levin; Manohar Castelino
> Cc: kata-hypervisor at lists.katacontainers.io
> Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype
>
> "Jessie Frazelle (TUPPERWARE)" <jessfraz at microsoft.com> writes:
>
>> Anthony,
>>
>> Would you be willing to dedicate resources to a _hypothetical_ rewrite
>> of that layer that we could replace qemu with in the form of a go
>> library?
>>
>> 0:)
>
> Go is so 2015.  Rust is where it's at now :-)
>
> In all seriousness, I've always felt strongly that a device model needs
> to avoid garbage collection.  While it's not strictly a real time
> system, OSes have an expectation that PIO or MMIO operations have an
> upper bound of latency.
>
> The other challenge with Go is unpredictable memory usage due to
> automatic heap growth.  If you want to do planning around density, being
> able to rationalize about the memory overhead from the VMM layer is
> pretty important.
>
> Regards,
>
> Anthony Liguori
>
>>
>>
>>
>> ________________________________________
>> From: Anthony Liguori <aliguori at amazon.com>
>> Sent: Wednesday, June 6, 2018 5:00 PM
>> To: Ernst, Eric; Sasha Levin; Manohar Castelino
>> Cc: kata-hypervisor at lists.katacontainers.io
>> Subject: Re: [Kata-hypervisor] Link to the Hypervisor Prototype
>>
>> "Ernst, Eric" <eric.ernst at intel.com> writes:
>>
>>> Hey Sasha, Anthony –
>>>
>>> I want to set a bit of context here.  At the face to face discussion
>>> in Vancouver, we had agreed to share the prototyping we have put in
>>> place to better understand how far we could go to remove legacy, and
>>> minimize the number of device models, while still booting key
>>> workloads.  Manohar’s response is to address the action that everyone
>>> in the meeting requested.
>>
>> Yup, appreciate the sharing and am disappointed I wasn't able to attend
>> in person.  I'm sure Paolo gave you lots of great feedback but let me
>> expand a bit on why I think this is the wrong approach.  Ultimately, you
>> are certainly free to continue down this path though but just thought
>> you may find this useful.
>>
>> The pieces of QEMU that are easy to remove are largely already
>> configurable at build time.  From a practical perspective, if you build
>> your "prototype" and measure the resulting executable size compared to a
>> minimalistic configuration, you will find very little actual reduction
>> in code.
>>
>> The stuff that's hard to remove is deeply ingrained (like QMP and QOM)
>> or parts that are just hairy (like vl.c).  Years of effort have gone
>> into decoupling these bits.
>>
>> So you get very little actual benefit (in code size reduction) by
>> forking but get to bare the burden of independent maintenance.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>
>>>
>>> Cheers,
>>> Eric
>>>
>>> On 6/6/18, 1:46 PM, "Sasha Levin" <Alexander.Levin at microsoft.com> wrote:
>>>
>>>     On Wed, Jun 06, 2018 at 08:08:46PM +0000, Castelino, Manohar R wrote:
>>>     >Folks,
>>>     >
>>>     >Please find below the link to the initial prototype code that tries to reduce the number of emulated devices in QEMU that can still boot most cloud workloads.
>>>     [snip]
>>>
>>>     Out of curiousity, have you looked at kvmtool
>>>     (https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kernel.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fwill%2Fkvmtool.git%2F&data=02%7C01%7Cjessfraz%40microsoft.com%7C604dbe2ada034e62d2f908d5cbf07f6b%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636639156156262890&sdata=xEWVp9B0rIFl5Ez1cGTMz9ClFs5Ril%2FTJN2SgVta824%3D&reserved=0)?
>>>
>>>     Forking qemu rather than building on top of it (or using something else)
>>>     isn't going to end well IMO.
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