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Re: [Xen-devel] vnuma toolstack extension request

On mer, 2014-09-24 at 11:24 -0400, Elena Ufimtseva wrote:

> On Wed, Sep 24, 2014 at 11:15 AM, Konrad Rzeszutek Wilk
> <konrad.wilk@xxxxxxxxxx> wrote:

>         Hey Elena,
> Hi Konrad
Hi Elena and Konrad,
>         Before you invest time in this, a couple of questions:
>          - Dariof was interested in merging this with his auto NUMA
>         placement code.
>            That piece of code does not look simple and I think he
>         volunteered
>            to do it. 
Not a piece of cake, definitely, mostly because of the many possible
ways the two things (vNUMA topology and automatic placement) can
interact and influence each others.

>         However he has also been busy reviewing Xen RT patches so
>            I figured he hasn't yet done that.
Exactly. I'm actually mostly done with it, but it needs a bit of
refining of a couple of rough edges, and for sure some testing, and,
once posted, integration with the other toolstack changes Elena has done
while addressing review comments, and then of course re-reviewing.

> Yes, Dario mentioned he will be working on this.
And I was, but as Konrad guessed, reviewing and testing the RT
scheduling stuff ate some time.

Also, consider that I'm about to disappear for at least two weeks,
starting (most likely) from next Monday, for (good :-) ) family reasons.
That means I probably won't be able to review/help with any future
version of the series.

Of course I'm no maintainer, I know, so that is not a showstopper
per-se. I'm just saying I think I could have been of help, while I
probably won't. :-)

>          - Since it would interact with auto NUMA placement and expose
>         new
>            logic in libxl we run in the problem of the 'stable' API
>         that we
>            MUST preserve. That is a worry - and will require
>         scrutinity.

>          - What is the impact if the toolstack patches go in Xen 4.6?
FWIW, my personal opinion is that we better actually defer this to 4.6.
> Maybe maintainers will have more info about this. I am only aware of
> that
> vNUMA will not be supported by toolstack in 4.5, so some related work
> will not be merged 
> as vNUMA aware ballooning and HVM support (not sure if the last one is
> happening though).
Yes, true, this is a rather basic building block of more general vNUMA
support. However, this also mean that, even if we merge it, we would
only have part of the picture in place for 4.5 anyway. I.e., we can work
on 4.6 to have all the vNUMA bits and pieces, and make a really big fuss
about that when releasing! :-)

This does not mean I would not have liked to have it there (given all
the effort that Elena, and recently Wei, put into it), but I guess this
is how software development work, isn't it? :-/

So, in summary, my take on this is: a lot of progress has been made,
which was not obvious, at least at some point. It's not yet ready, but
that only mean 4.6 will be a great release wrt vNUMA!! :-D


<<This happens because I choose it to happen!>> (Raistlin Majere)
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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