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I recently purchased a Xeon E3 1270 to upgrade an older LGA1155 desktop I am using as a Plex server on Ubuntu. The previous CPU was an I5-2400. I did not reinstall Ubuntu. Instead, I just ran:

update -initramfs -u -k all

as root after installing the "new" cpu.

Good news, the server boots and works! Yay! My challenge is, I'm not sure if the CPU is properly being utilized. According to https://ark.intel.com, this should be a 4 core, 8 thread CPU. However, when I run lscpu it only indicates 1 thread per core.

So, do I need to reinstall Ubuntu from scratch to get it to recognize the additional threads? Did I somehow get ripped off in the CPU purchase and this is not an actual E3 1270 with 8 threads?

Thanks for any help. I'm using Ubuntu 18.04 LTS Server.

Here is what lscpu displays:

Architecture:        x86_64 <br>
CPU op-mode(s):      32-bit, 64-bit<br>
Byte Order:          Little Endian<br>
CPU(s):              4<br>
On-line CPU(s) list: 0-3<br>
Thread(s) per core:  1<br>
Core(s) per socket:  4<br>
Socket(s):           1<br>
NUMA node(s):        1<br>
Vendor ID:           GenuineIntel<br>
CPU family:          6<br>
Model:               42<br>
Model name:          Intel(R) Xeon(R) CPU E31270 @ 3.40GHz<br>
Stepping:            7<br>
CPU MHz:             1619.944<br>
CPU max MHz:         3800.0000<br>
CPU min MHz:         1600.0000<br>
BogoMIPS:            6784.83<br>
Virtualization:      VT-x<br>
L1d cache:           32K<br>
L1i cache:           32K<br>
L2 cache:            256K<br>
L3 cache:            8192K<br>
NUMA node0 CPU(s):   0-3<br>
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    did you check your BIOS settings? Typically hyper-threading can be enabled/disabled there, although there are other places also. Commented Aug 11, 2020 at 23:51
  • "I did not reinstall Ubuntu." - you made a significant hardware change. Reinstall the OS. Maybe run a live session first to see if all the threads are being used.
    – Nmath
    Commented Aug 12, 2020 at 1:03
  • 1
    I agree with the first commenter. The linux kernel will use what it can. No reinstall needed Commented Aug 12, 2020 at 1:22

2 Answers 2

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to know the number of cores, you can use: nproc

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Thankyou for the reminder to check the BIOS Doug! I was sure I had it on there. Nope. So finding Hyper-Threading in the BIOS and enabling it did it!

I ran update -initramfs -u -k all again. Not sure if that was necessary. However, now htop shows all 8 threads working and lscpu reads:

Architecture:        x86_64 <br>
CPU op-mode(s):      32-bit, 64-bit<br>
Byte Order:          Little Endian<br>
CPU(s):              8<br>
On-line CPU(s) list: 0-7<br>
Thread(s) per core:  2<br>
Core(s) per socket:  4<br>
Socket(s):           1<br>
NUMA node(s):        1<br>
Vendor ID:           GenuineIntel<br>
CPU family:          6<br>
Model:               42<br>
Model name:          Intel(R) Xeon(R) CPU E31270 @ 3.40GHz<br>
Stepping:            7<br>
CPU MHz:             2659.406<br>
CPU max MHz:         3800.0000<br>
CPU min MHz:         1600.0000<br>
BogoMIPS:            6784.79<br>
Virtualization:      VT-x<br>
L1d cache:           32K<br>
L1i cache:           32K<br>
L2 cache:            256K<br>
L3 cache:            8192K<br>
NUMA node0 CPU(s):   0-7<br>

Thanks so much for the tip to go back into the BIOS. Feeling sheepish that I did not thoroughly go there first, but thanks!

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