kernel reporting incorrect CPU count

Question

It is Ubuntu 16.04

$ uname -a
Linux m-x170 4.4.0-42-generic #62-Ubuntu SMP Fri Oct 7 23:11:45 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

The processor used is Xeon E3 1245 v5 that is spec'ed as quad core 8 threads per core.

dmidecode -t processor shows

Core Count: 4
Core Enabled: 4
Thread Count: 8
Characteristics:
    64-bit capable
    Multi-Core
    Hardware Thread
    Execute Protection
    Enhanced Virtualization
    Power/Performance Control

And lscpu shows

$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                8
On-line CPU(s) list:   0-7
Thread(s) per core:    2
Core(s) per socket:    4
Socket(s):             1
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 94
Model name:            Intel(R) Xeon(R) CPU E3-1245 v5 @ 3.50GHz

And when queried about HTT, it is there too.

$ sudo dmidecode | grep HTT
        HTT (Multi-threading)

The question is: Why is lscpu showing 2 threads per core where as the dmidecode reports 8 threads (meaning 8 per core)?

Answer 1

You have 4 CPU cores, with Hyper Threading (HTT) support you have one additional logical core per CPU.

So you have:

• 4 physical cores
• 8 logical cores

and the results of the commands are correct.

Answer 2

No, dmidecode reports 8 threads in total, which means 2 threads on each of the 4 cores.