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Re: [Xen-devel] Xen 3.4.1 NUMA support

To: Juergen Gross <juergen.gross@xxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Xen 3.4.1 NUMA support
From: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
Date: Mon, 9 Nov 2009 12:07:50 +0000
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, Papagiannis Anastasios <apapag@xxxxxxxxxxxx>
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On Mon, Nov 9, 2009 at 11:44 AM, Juergen Gross
<juergen.gross@xxxxxxxxxxxxxx> wrote:
> George, would this be okay for you? I think your scheduler still will have
> problems with domain weights as long as domains are restricted to some
> processors, right?

Hmm, this may be a point of discussion at some point.

My plan was actually to have one runqueue per L2 processor cache.
Thus as many as 4 cores (and possibly 8 hyperthreads) would be sharing
the same runqueue; doing CPU pinning within the same runqueue would be

I was planning on having credits work mainly within one runqueue, and
then do load balancing between runqueues.  In that case pinning to a
specific runqueue shouldn't cause a problem, because credits of one
runqueue wouldn't affect credtis of another one.

However, I haven't implemented or tested this idea yet; it's possible
that having credits kept distinct and doing load balancing between
runqueues will cause unacceptable levels of unfairness.  I expect it
to be fine (esp since Linux's scheduler does this kind of load
balancing, but doesn't share runqueues between logical processors),
but without implementation and testing I can't say for sure.

Thoughts are welcome at this point, but it will probably be better to
have a real discussion once I've posted some patches.


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