Bug 810580 - AMD Magny-cours processors have wrong topology
AMD Magny-cours processors have wrong topology
Product: Virtualization Tools
Classification: Community
Component: libvirt (Show other bugs)
x86_64 Linux
unspecified Severity medium
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Assigned To: Libvirt Maintainers
Depends On:
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Reported: 2012-04-06 16:41 EDT by Tad Kollar
Modified: 2016-03-23 17:02 EDT (History)
4 users (show)

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Fixed In Version:
Doc Type: Bug Fix
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Last Closed: 2016-03-23 17:02:35 EDT
Type: Bug
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RHEL 7.3 requirements from Atomic Host:
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Description Tad Kollar 2012-04-06 16:41:13 EDT
Description of problem:
Magny-cours processors with 12 cores per physical socket should be detected as either having one socket and 12 cores, or possibly two sockets with 6 cores each. Instead they are detected as one socket and six cores, so only half the cores are usable by libvirt.

Version-Release number of selected component (if applicable):
0.9.11, 0.9.10, and possibly more after 0.9.4.

How reproducible:

Steps to Reproduce:
1. Run virsh capabilities on a host with an AMD Opteron 6174 or similar processor
2. Examine the topology entry
Actual results:

      <topology sockets='4' cores='6' threads='1'/>

Expected results:

      <topology sockets='4' cores='12' threads='1'/>

Additional info:
There seems to be confusion between the topology reported by numa and the physical topology that's causing the problem. Numa detects 8 sockets with 6 cores each, yet there are four physical sockets with 12 cores. The issue did not exist in libvirt 0.9.4.
Comment 1 Cole Robinson 2016-03-23 17:02:35 EDT
Sorry this never received a response. I'm not sure if this was ever fixed since I don't have that system. If you can still reproduce with newer libvirt please reopen this bug and provide /proc/cpuinfo

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