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RE: [Xen-devel] Xen 3.4.1 NUMA support

To: Jan Beulich <JBeulich@xxxxxxxxxx>, Andre Przywara <andre.przywara@xxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: RE: [Xen-devel] Xen 3.4.1 NUMA support
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Date: Tue, 10 Nov 2009 01:46:41 +0000
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Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <Keir.Fraser@xxxxxxxxxxxxx>, Papagiannis Anastasios <apapag@xxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Xen 3.4.1 NUMA support
> >>> Andre Przywara <andre.przywara@xxxxxxx> 09.11.09 16:02 >>>
> >BTW: Shouldn't we set finally numa=on as the default value?
> I'd say no, at least until the default confinement of a guest to a single
> node gets fixed to properly deal with guests having more vCPU-s than
> a node's worth of pCPU-s (i.e. I take it for granted that the benefits of
> not overcommitting CPUs outweigh the drawbacks of cross-node memory
> accesses at the very least for CPU-bound workloads).

What default confinement? I thought guests had an all-pCPUs affinity mask be 

I suspect we will get benefits enabling NUMA even if all the guests have 
all-pCPUs affinity masks: all guests will have memory stripped across all 
nodes, which is likely better than allocating from one node and then the other. 
Obviously assigning VMs to node(s) and allocating memory accordingly is the 
best plan.


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