I got a bug report yesterday that seems to be related to how CPUs are ordered 'lscpu' and /proc/cpuinfo: https://bugzilla.redhat.com/show_bug.cgi?id=1351160 It's not an actual bug, but it's not the first time I see people confused by CPU numbers not following socket/core/thread IDs in lscpu and /proc/cpuinfo in the host (making CPU numbers seen in the guest not matching CPU numbers in the host). The ordering in /proc/cpuinfo and lscpu seems to come from the MADT ACPI table, and on some hosts it looks completely arbitrary[1]. Now that we will allow the APIC ID (or socket/core/thread IDs) to be explicitly set in each VCPU, we could let management make CPU ordering match the host exactly, for people that really want to reproduce the host topology and get easily confused by CPU numbers that don't match the host. But this is lot of data to be provided to QEMU, so I don't see it as an useful feature unless it can be represented in the libvirt XML configuration in a more compact way, or generated automatically based on the host. I'm CCing libvir-list to see if they have any ideas. ...or we could just tell users that sometimes it will be impossible to make the CPU numbers in the guest match the ones in the host. To be honest, I am more inclined towards this option, but I would like to hear your opinions. [1] Example of lscpu output from a host that doesn't follow socket/core/thread ID on the MADT table: # lscpu -e CPU NODE SOCKET CORE L1d:L1i:L2:L3 ONLINE 0 1 0 0 0:0:0:0 yes 1 0 1 1 1:1:1:1 yes 2 1 0 2 2:2:2:0 yes 3 0 1 3 3:3:3:1 yes 4 1 0 4 4:4:4:0 yes 5 0 1 5 5:5:5:1 yes 6 1 0 6 6:6:6:0 yes 7 0 1 7 7:7:7:1 yes 8 1 0 8 8:8:8:0 yes 9 0 1 9 9:9:9:1 yes 10 1 0 10 10:10:10:0 yes 11 0 1 11 11:11:11:1 yes 12 1 0 0 0:0:0:0 yes 13 0 1 1 1:1:1:1 yes 14 1 0 2 2:2:2:0 yes 15 0 1 3 3:3:3:1 yes 16 1 0 4 4:4:4:0 yes 17 0 1 5 5:5:5:1 yes 18 1 0 6 6:6:6:0 yes 19 0 1 7 7:7:7:1 yes 20 1 0 8 8:8:8:0 yes 21 0 1 9 9:9:9:1 yes 22 1 0 10 10:10:10:0 yes 23 0 1 11 11:11:11:1 yes # lscpu Architecture: x86_64 CPU op-mode(s): 32-bit, 64-bit Byte Order: Little Endian CPU(s): 24 On-line CPU(s) list: 0-23 Thread(s) per core: 2 Core(s) per socket: 6 Socket(s): 2 NUMA node(s): 2 Vendor ID: GenuineIntel CPU family: 6 Model: 44 Model name: Intel(R) Xeon(R) CPU L5640 @ 2.27GHz Stepping: 2 CPU MHz: 2266.000 BogoMIPS: 4533.26 Virtualization: VT-x L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 12288K NUMA node0 CPU(s): 1,3,5,7,9,11,13,15,17,19,21,23 NUMA node1 CPU(s): 0,2,4,6,8,10,12,14,16,18,20,22 # -- Eduardo