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I have a few servers with Dual E5-2680 v2 CPUs on Ubuntu 18.04. Each E5-2680 v2 has 10 physical cores or 20 threads. That being said, running "cat /proc/cpuinfo | grep processor | wc -l" should show 40.

However, some servers shows only 20. For these servers, output of command

cat /proc/cpuinfo | grep "physical id"

physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 0
physical id : 1
physical id : 1
physical id : 1
physical id : 1
physical id : 1
physical id : 1
physical id : 1
physical id : 1
physical id : 1
physical id : 1

user@hostname:~# lscpu

Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
CPU(s):              20
On-line CPU(s) list: 0-19
Thread(s) per core:  1
Core(s) per socket:  10
Socket(s):           2
NUMA node(s):        2
Vendor ID:           GenuineIntel
CPU family:          6
Model:               62
Model name:          Intel(R) Xeon(R) CPU E5-2680 v2 @ 2.80GHz
Stepping:            4
CPU MHz:             1200.814
CPU max MHz:         3600.0000
CPU min MHz:         1200.0000
BogoMIPS:            5600.17
Virtualization:      VT-x
L1d cache:           32K
L1i cache:           32K
L2 cache:            256K
L3 cache:            25600K
NUMA node0 CPU(s):   0-9
NUMA node1 CPU(s):   10-19
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm cpuid_fault epb pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid fsgsbase smep erms xsaveopt dtherm ida arat pln pts flush_l1d

Do you have an idea what could cause this problem? Thanks.

2

As you're seeing two differnt physical ids, both CPUs seem to be enabled.

However, if hyperthreading has been disabled in System Setup (i.e. "BIOS"), you will just see one"thread" per CPU core and not two. Resulting in 20 CPUs in /proc/cpuinfo instead of the expected 40. Once you enable hyperthreading in the CPU configuration screen of your System Setup, you should then see 40 CPUs in /proc/cpuinfo.

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