Re: [PATCH v3 1/4] xen: add real time scheduler rtds

[Dario Faggioli <dario.faggioli@citrix.com>]

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On ven, 2014-09-19 at 12:44 -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, Sep 18, 2014 at 05:08:45PM +0100, George Dunlap wrote:

> > deadline, and then address the things I'm bringing up here?  Or would it be
> > better to wait until all the issues are sorted and then check it in (even if
> > it's after the deadline)?
> 
> We can check it in after the deadline - and have those issues resolved.
> 
FWIW, I think the series looks good now, and in fact I sent in my
Reviewed-by for all of it.

> I am basing this on the assumption that:
>  - The risks of regressions to the rest of schedulers is nill (as this is all
>    new codepaths (as this is all
>  - The risks of regressions to the rest of the code-base is nill (as this is all
>    new).
>  - The resolution of the 'couple of things' are not going to lead to more
>    'couple of things' and lead to re-design.
>
This is all true, IMO.

> The common code that is touched does not look scary to me. And both of the
> scheduler maintainers -  you and Dariof are OK with the design and the patchset
> (minus the 'couple of things').
> 
Exactly.

> Are we aim to have this be experimental for Xen 4.5 or do we want this
> to be on the 'stable' ?
>
Not sure. What I'm sure about is that
1) the interface needs to change a bit, to include support for the
   per-vcpu parameters setting (although, that can happen in a
   backward compatible way, i.e., not touching or altering neither the
   look nor the semantic or the interface we'll be checking in if we
   take v4)
2) there is _a_lot_ to gain, from a performance point of view, and Meng
   already agreed on continuing working toward that, after 4.5

Having it in is, IMO, important, especially for the new
embedded/mobile/automotive uses of Xen we're seeing in these days (in
fact, I think GlobalLogic is using RT-Xen already, so the upstreaming of
this scheduler would be quite useful at least to them [correct me if I'm
wrong]).

However, given 2 above, if we mark it as stable, we risk that people
(mostly people not yet involved into Xen development and not on this
mailing list) would try it, run into non-optimal performance, and get
upset/angry. For that reason, I think I'd go for 'experimental for 4.5'.

Regards,
Dario

-- 
<<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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