[Patch] tools: improve NUMA guest placement when ballooning

[Andre Przywara <andre.przywara@amd.com>]

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Hi,

the "guest to a single NUMA node" constrain algorithm does not work well 
when we do ballooning. Ballooning and NUMA don't play together anyway, 
as Dom0 and thus ballooning is not NUMA aware, I am working on this but 
it will not be ready for the Xen 4.0 release window.
The usual ballooning situation will result in an empty candidate list, 
as no node has enough free memory to host the guest. In this case the 
code will simply pick the first node: again and again, because all nodes 
without enough memory will be ultimately penalized with the same maxint 
value (regardless of the actual load).
The attached patch will change this to use a relative penalty in case of 
not-enough memory, so that low-load low-memory nodes will be used at one 
point. A half loaded node has shown to be a good value, as an unbalanced 
system is much worse than non-local memory access for guests.
Regardless of that you should restrict the Dom0 on a NUMA system to a 
reasonable memory size, so that ballooning is not necessary most of the 
time. In this case the guest's memory will be NUMA local.

Signed-off-by: Andre Przywara <andre.przywara@amd.com>

Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
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Advanced Micro Devices GmbH
Karl-Hammerschmidt-Str. 34, 85609 Dornach b. Muenchen
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diff -r 8f304c003af4 tools/python/xen/xend/XendDomainInfo.py
--- a/tools/python/xen/xend/XendDomainInfo.py	Wed Dec 09 10:59:31 2009 +0000
+++ b/tools/python/xen/xend/XendDomainInfo.py	Thu Dec 10 15:04:41 2009 +0100
@@ -2639,10 +2639,9 @@
                                     nodeload[i] += 1
                                     break
                 for i in range(0, nr_nodes):
-                    if len(info['node_to_cpu'][i]) > 0 and i in node_list:
-                        nodeload[i] = int(nodeload[i] * 16 / len(info['node_to_cpu'][i]))
-                    else:
-                        nodeload[i] = sys.maxint
+                    nodeload[i] = int(nodeload[i] * 16 / len(info['node_to_cpu'][i]))
+                    if len(info['node_to_cpu'][i]) == 0 or i not in node_list:
+                        nodelist[i] += 8
                 return map(lambda x: x[0], sorted(enumerate(nodeload), key=lambda x:x[1]))
 
             info = xc.physinfo()

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