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[Xen-devel] Re: Ping: c/s 20526 (tools: avoid cpu over-commitment if num

To: Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: [Xen-devel] Re: Ping: c/s 20526 (tools: avoid cpu over-commitment if numa=on)
From: Andre Przywara <andre.przywara@xxxxxxx>
Date: Wed, 13 Jan 2010 15:24:35 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
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Jan Beulich wrote:
Andre,

I'm afraid this change isn't really correct:

+                cores_per_node = info['nr_cpus'] / info['nr_nodes']
+                nodes_required = (self.info['VCPUs_max'] + cores_per_node - 1) 
/ cores_per_node

Simply using cores_per_node (as calculated here) as a divisor is bound
to cause division-by-zero issues, namely when limiting the number of
CPUs on the Xen command line (maxcpus=). I'm not sure though, what
a reasonable solution to this might look like, since cores-per-node is
a meaningless thing in an artificial setup like this, and may also be
meaningless in asymmetric configurations. So perhaps we really need
to iterate over nodes while summing up the number of CPUs they
have until the number of needed vCPU-s was reached.
Thanks for the heads-up. I have created a better patch basically doing what you described, actually it is even more elegant than the original version. I am about to test it and will send it out as soon as the testing is finished.

Regards,
Andre.

--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
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