I can confirm this. Most of our hosts have 64GB RAM and 2 Intel Nehalem hexa-cores. With 3 VM's using 16GB RAM each. I noticed performance degredation and the host also swapped out a lot of memory. The swapping degraded performance dramatically. vm.swappiness=0 in /etc/sysctl.conf did not help.
It seems that NUMA on Intel CPU's can be expensive because RAM needs to be transfered from other nodes. With only 1 node (socket) there is no problem. With 2 or more nodes you see slower. Without the capabilities you can prevent this behavior by pinning the vcpu's. You should spread you VM's over the available nodes: numactl --hardware | grep "node 0 cpus" node 0 cpus: 0 2 4 6 8 10 12 14 16 18 20 22 Your XML should contain something like this: <vcpu cpuset='0,2,4,6,8,10,12,14,16,18,20,22'>1</vcpu> <vcpu cpuset='0,2,4,6,8,10,12,14,16,18,20,22'>2</vcpu> <vcpu cpuset='0,2,4,6,8,10,12,14,16,18,20,22'>3</vcpu> <vcpu cpuset='0,2,4,6,8,10,12,14,16,18,20,22'>4</vcpu> The next VM should use they other node. numactl --hardware | grep "node 1 cpus" node 0 cpus: 1 3 5 7 9 11 13 15 17 19 21 23 <vcpu cpuset='1,3,5,7,9,11,13,15,17,19,21,23'>1</vcpu> <vcpu cpuset='1,3,5,7,9,11,13,15,17,19,21,23'>2</vcpu> <vcpu cpuset='1,3,5,7,9,11,13,15,17,19,21,23'>3</vcpu> <vcpu cpuset='1,3,5,7,9,11,13,15,17,19,21,23'>4</vcpu> So you don't need the NUMA info from "virsh capabilities". We now split up our hosts by the amount of NUMA-nodes to prevent performance-degradation and swapping. -- libvirt not recognizing NUMA architecture https://bugs.launchpad.net/bugs/614322 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs