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CPU overcommit not working with Devstack installation

asked 2013-12-04 13:23:12 -0500

btully80 gravatar image

Hello All,

I've just intalled a single node devstack configuration on a dual core system and I am only seeing 2 vCPUs for the hypervisor. According to my research nova should default to a 16:1 overcommit ratio per core. I was expecting to see 32 vCPUs. Do I need to enable CPU overcommit or is on by default? If it needs to be enabled what would the devstack localrc attribute be?

root@openstack01:~# lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 2 On-line CPU(s) list: 0,1 Thread(s) per core: 1 Core(s) per socket: 2 Socket(s): 1 NUMA node(s): 1 Vendor ID: GenuineIntel CPU family: 6 Model: 23 Stepping: 10 CPU MHz: 2935.000 BogoMIPS: 5847.74 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 6144K NUMA node0 CPU(s): 0,1

stack@openstack01:~/devstack$ nova hypervisor-show openstack01.lab.dom | grep cpu_info | cpu_info | {"vendor": "Intel", "model": "Penryn", "arch": "x86_64", "features": ["osxsave", "xsave", "pdcm", "xtpr", "tm2", "est", "smx", "vmx", "ds_cpl", "monitor", "dtes64", "pbe", "tm", "ht", "ss", "acpi", "ds", "vme"], "topology": {"cores": 2, "threads": 1, "sockets": 1}} | stack@openstack01:~/devstack$

Many thanks, Brian Tully

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answered 2013-12-04 21:38:09 -0500

fifieldt gravatar image

Overcommit is implemented at the scheduler level. Just try running more than 2 cores worth of VMs and it should work fine.

cpu_allocation_ratio is 16.0 by default - as you've noted.

In short - no problem. Those commands you're running are just showing the physical CPUs, as expected.

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answered 2014-01-28 15:49:38 -0500

Also look at the other resources as in disk and memory and make sure you not over running those. On one my devstack installs which is a small dual core laptop, 4g memory, I can launch 20 m1.nano vm's but it takes the machine over completely.

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Asked: 2013-12-04 13:23:12 -0500

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Last updated: Jan 28 '14