Re: [Xen-devel] [Hackathon Minutes] Xen 4.4 Planning

[Ian Murray <murrayie@xxxxxxxxxxx>]

On 13/06/13 22:03, Alex Bligh wrote:
> --On 13 June 2013 15:00:46 +0100 Lars Kurth <lars.kurth@xxxxxxx> wrote:
>
> > We should aim to reduce the release cycle to 4 months (or maybe 6 months
> > as an intermediate step) from the current 9 months. A 4 months relase
> > cycle should help accelerate development and lead to fewer patches being
> > queued up. The implications are that we would have to operate a 2-3 
> > weeks
> > merge window.
> Disclaimer: I don't claim to be a xen developer, despite writing a few
> patches. But we are a heavy libxl API user. This perspective may or may
> not be useful from a 'consumer of your development' perspective. Delete
> or ignore if not.
>
> The thing we like the least about Xen is (was?), stuff breaking between
> major releases. If you have to drop 90% of your new features in order
> not to break stuff, please do just that. Xen 3.x -> Xen 4.1 (we mostly
> skipped 4.0) was a huge change, requiring a lot of rewriting. Xen 4.1
> to Xen 4.2 was far, far worse; had we not needed it to support
> qemu-upstream, we'd have probably stuck with 4.1. We talk to 4 
> hypervisors,
> and have never had this difficulty with any other hypervisor. You can
> imagine our joy when we found we could compile against 4.3 (we haven't
> tried running yet) without a single line code changed. Please, please,
> keep it like this. If we can also run unchanged against 4.3, this will
> be even better.
When you talk about "stuff" breaking between major releases, are you 
talking about Xen code not functioning or your code failing because of 
changes in Xen? If the latter, are we talking designed changes in Xen's 
behaviour or non-designed ones (=bugs)?

> The thing we like the second least about Xen is how long it seems to take
> to get what we count as serious bugs fixed, even in stable releases. We
> like it even less if we have to find them and fix them. By 'serious'
> I mean basic functionality not working, crashes dom0, etc. I don't know
> if this says something bad about us, but we've not found any such bug
> ever in kvm (in well over 5 years). On the positive side, we've found
> xen-devel pretty friendly and receptive. The perception is, however, that
> new development takes priority over stable releases. I recognise that I
> have a bias here, so this may not be fair.
I am at a loss as to what is wrong with contributing a few bug fixes 
back if you're technically capable of finding and fixing... I am not 
feeling the community spirit here.
> The result of this is two-fold. Firstly, we've never (yet) been able to
> run a production version of xen which is a standard xen release. We've
> always had to maintain our own patches even on 'stable' releases.
> Frankly, this is a pain. Secondly, there is a perception that moving
> versions of Xen is going to be a huge PITA; that perception does not
> exist for other hypervisors. I'm really really hoping Xen 4.3 dispels
> this, and signs are good so far (we've done a lot of testing at xl
> level, not so much at libxl level).
I thought Xen was a "project" not a "product".

Also, a little bit of Googling tells me that Flexiant (that is the "we" 
in all of this, right?) provides cloud software to third-parties and 
does not provide cloud services itself. To make your product work 
reliably with Xen for your customers, are you distributing your own 
patches for Xen to these third-parties?


> What does this mean for the development process?
>
> 1. I think more testing would be useful, particularly against API driven
>   stuff. I find the current test stuff a bit confusing. What I wan't
>   to know is whether commit X works or not - if things fail randomly,
>   they aren't useful tests, particularly if it's difficult to
>   distinguish them from other failures. Spoken as someone who's broken
>   things :-(
>
> 2. My concern about early branching of -next (at -rc1 for instance) is
>   that developing new stuff is far more interesting than fixing bugs.
>   We liked the way stuff we raised with 4.3 (e.g. tsc issues) got looked
>   at, and would hope that continues.
>
> 3. I would quite like a slightly shorter development cycle IFF it
>   doesn't impact on stability. EG I thought we were probably bending the
>   rules to get live migrate on qemu-upstream backported into 4.2,
>   and had 4.3 been available sooner, we wouldn't have pushed. At
>   a guess, 6 months would be about right, 4 months would be too short.
>
> 4. Following xen has been 10 times easier since you've moved to git.
>   I agree with George's statement that you aren't using it enough -
>   particularly branches.
>
> 5. At risk of repetition, we don't really care, so long as you don't 
> break
>   stuff.
Again, what "stuff"? IMHO woolly language isn't wonderfully helpful in 
most cases, especially on a technical list.
Thanks for reading.

Disclosure: An interested individual who was delighted to recently have 
had a tincy-wincy patch accepted into unstable, fixing a bug that has 
annoyed me for donkey's.
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