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Re: [Xen-devel] [PATCH 08 of 10 v3] libxl: enable automatic placement of guests on NUMA nodes

On 06/07/12 15:35, Dario Faggioli wrote:
On Fri, 2012-07-06 at 14:05 +0100, George Dunlap wrote:
Ok, I get this like I can leave it as it is... Or you want me to kill
the sorting?
I can't really foresee a time when anyone would want to use anything
other than the best option.

Well, perhaps being able to do some more fiddling, like<<now that I
have all the ones that meet _THESE_ characteristics, and I have them in
_THAT_ precise ordering, let's pick up the first that meets _THIS_OTHER_

Anyway, it might well be over-thinking the whole thing. In my first RFC,
when I was introducing more placement policies (and the respective user
interfaces and configuration bits), I was exploiting the fact that, like
this, I never loose access to the full list of candidates, so, maybe
when/if that will be the case again (during 4.3 dev cycle) everything
will be more clear.

As soon as we'll have a better picture of what feature and what
interface we want this whole placement thing to have, what kind of users
and behaviour we want to support (e.g., what libvirt does and what does
it require wrt NUMA placement), we could better decide what to do.
That's the benefit of having all this internally and not exported in any
means yet (a benefit for which I give you and Ian all the credits :-P).

Just choosing the best makes a slightly
simpler interface, and simplified the code somewhat.

I can't and am not going to argue against that, as I think that too.

At the moment,
sorting shouldn't take too long, but suppose we get systems with 128
nodes at some point in the future -- then the number of possible
combinations might be pretty large, and sorting that even at n log n
might take a noticeable amount of time.


So I think it's up to you: If you thinking sorting will be useful in the
future, then I think keep it.  But if you also think it's not going to
be very useful, I think it would make more sense to take it out.

As we agreed elsewhere in the thread, let's keep it like this for now,
and see how it behaves. I'll keep an eye at it, and won't push for
keeping sort() instead of max() if shows to not provide any benefit.
OK -- then I think we have a go-ahead to check in patches 8 and 9 (with perhaps some changes to wording of some comments?).


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