Understanding output of lscpu

Question

You can see the output from lscpu command -

jack@042:~$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                56
On-line CPU(s) list:   0-55
Thread(s) per core:    2
Core(s) per socket:    14
Socket(s):             2
NUMA node(s):          2
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 79
Model name:            Intel(R) Xeon(R) CPU E5-2690 v4 @ 2.60GHz
Stepping:              1
CPU MHz:               2600.000
CPU max MHz:           2600.0000
CPU min MHz:           1200.0000
BogoMIPS:              5201.37
Virtualization:        VT-x
Hypervisor vendor:     vertical
Virtualization type:   full
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              35840K
NUMA node0 CPU(s):     0-13,28-41
NUMA node1 CPU(s):     14-27,42-55

I can see that there are 2 sockets (which is like a processor ??) and inside each of the socket we have 14 cores. So, in total 2x14=28 physical cores. Normally, a CPU can contain multiple cores, so number of CPUs can never be smaller than number of Cores. But, as shown in the output CPUs(s): 56 and this is what is confusing me.

I can see that Thread(s) per core: 2, so these 28 cores can behave like 2x28=56 logical cores.

Question 1: What does this CPUs(s): 56 denote? Does CPU(s) denote number of Virtual/Logical core, as it cannot be a Physical core core atleast?

Question 2: What does this NUMA node mean? Does it represent the socket?

Answer 1

“CPU(s): 56” represents the number of logical cores, which equals “Thread(s) per core” × “Core(s) per socket” × “Socket(s)”. One socket is one physical CPU package (which occupies one socket on the motherboard); each socket hosts a number of physical cores, and each core can run one or more threads. In your case, you have two sockets, each containing a 14-core Xeon E5-2690 v4 CPU, and since that supports hyper-threading with two threads, each core can run two threads.

“NUMA node” represents the memory architecture; “NUMA” stands for “non-uniform memory architecture”. In your system, each socket is attached to certain DIMM slots, and each physical CPU package contains a memory controller which handles part of the total RAM. As a result, not all physical memory is equally accessible from all CPUs: one physical CPU can directly access the memory it controls, but has to go through the other physical CPU to access the rest of memory. In your system, logical cores 0–13 and 28–41 are in one NUMA node, the rest in the other. So yes, one NUMA node equals one socket, at least in typical multi-socket Xeon systems.