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[Xen-devel] [Patch] tools: improve NUMA guest placement when ballooning

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] [Patch] tools: improve NUMA guest placement when ballooning
From: Andre Przywara <andre.przywara@xxxxxxx>
Date: Thu, 10 Dec 2009 15:07:55 +0100
Delivery-date: Thu, 10 Dec 2009 06:08:48 -0800
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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@xxxxxxx>


Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448 3567 12
----to satisfy European Law for business letters:
Advanced Micro Devices GmbH
Karl-Hammerschmidt-Str. 34, 85609 Dornach b. Muenchen
Geschaeftsfuehrer: Andrew Bowd; Thomas M. McCoy; Giuliano Meroni
Sitz: Dornach, Gemeinde Aschheim, Landkreis Muenchen
Registergericht Muenchen, HRB Nr. 43632
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
                 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 / 
-                    else:
-                        nodeload[i] = sys.maxint
+                    nodeload[i] = int(nodeload[i] * 16 / 
+                    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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