Comment 2 for bug 1467927

Before considering the placement on the host OS, you need to consider the topology exposed to the guest OS

For a 3 vCPU guests there are 3 possible topologies

 - 1 socket, 1 core, 3 threads
 - 1 socket, 3 cores, 1 thread
 - 3 sockets, 1 core, 1 thread

In the description it does not mention any of the flavour / image settings for vCPU topology, so I'm assuming the testing was done with the defaults, which means 3 sockets, 1 core, 1 thread. Given that every vCPU would appear as a socket, Nova should not be attempting to prefer hyperthread siblings at all, because telling the guest that it has separate sockets, when in fact it is running on thread siblings would result in bad guest schedular decisions. The Nova schedular should only prefer pinning to hyperthread siblings in the host, if the guest topology also has been setup with hyperthreads.