AMD Epyc 3251 only showing 1 thread per core instead of two (ASROCK Rack EPYC3251D4I-2T)

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Janga

New Member
Sep 21, 2019
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I recently purchased two ASRock Rack EPYC3251D4I-2T motherboards with the AMD Epyc 3251 SoC CPU. This is a 8 core/16 thread CPU. Each system boots up and runs fine, however the CPU is only showing up as a 8 core/8 thread CPU (i.e. half the amount of threads it's meant to have). I have SMT (multithreading) enabled in the BIOS and have also updated the BIOS to the latest version (1.10) and also done a CMOS reset and it still only shows up as a 8 core/8 thread CPU. I have tried a number of different Linux distros and also Windows, and they all only see 1 thread per core, instead of two. With Linux I have also passed kernel parameters to enable multithreading (smt=2) but this doesn't change anything. Below is the output from lscpu. It clearly shows only 1 thread per core however the HT flag is also present indicated the CPU supports multithreading. I have two of these motherboards and they both indicating they only have 1 thread per core. I see STH has done a review previously on the Epyc 3251 and their lscpu out clearing shows it as having two threads per core.

https://www.servethehome.com/amd-epyc-3251-benchmarks-and-review/amd-epyc-3251-lscpu-output/

Motherboard specs:
ASRock Rack > EPYC3251D4I-2T

Any ideas why I'm only seeing half the amount of cores?

My output from lscpu.

root@pve:~# lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
Address sizes: 43 bits physical, 48 bits virtual
CPU(s): 8
On-line CPU(s) list: 0-7
Thread(s) per core: 1
Core(s) per socket: 8
Socket(s): 1
NUMA node(s): 1
Vendor ID: AuthenticAMD
CPU family: 23
Model: 1
Model name: AMD EPYC 3251 8-Core Processor
Stepping: 2
CPU MHz: 3029.677
CPU max MHz: 2500.0000
CPU min MHz: 1200.0000
BogoMIPS: 4990.28
Virtualization: AMD-V
L1d cache: 32K
L1i cache: 64K
L2 cache: 512K
L3 cache: 8192K
NUMA node0 CPU(s): 0-7
Flags: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt pdpe1gb rdtscp lm constant_tsc rep_good nopl nonstop_tsc cpuid extd_apicid aperfmperf pni pclmulqdq monitor ssse3 fma cx16 sse4_1 sse4_2 movbe popcnt aes xsave avx f16c rdrand lahf_lm cmp_legacy svm extapic cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb hw_pstate sme ssbd sev ibpb vmmcall fsgsbase bmi1 avx2 smep bmi2 rdseed adx smap clflushopt sha_ni xsaveopt xsavec xgetbv1 xsaves clzero irperf xsaveerptr arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif overflow_recov succor smca
 

Janga

New Member
Sep 21, 2019
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Just to provide an update, the motherboard supplier has supplied me with a beta firmware update they obtained from ASRock Rack. I flashed the BIOS with this firmware and now all 16 threads are visible in the BIOS and OS!

Hopefully it's just a matter of time before ASRock update the BIOS on there website for this board to fix this problem. What a weird bug to have half the CPU threads missing.
 
Last edited:

Evan

Well-Known Member
Jan 6, 2016
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Kind major function to be not working on a release product... very strange.
 

chn

New Member
Dec 22, 2019
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@Janga, are you able to share the BIOS you have for this? I'm currently on version 1.10, and my server also only shows 8 cores and 8 threads on the same motherboard.
 

LabMulch

New Member
Feb 22, 2018
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2 months later and they still haven't released the BIOS yet. Got the system for extremely cheap but didn't expect it to be such a neglected product.

Did you encounter any issues with the 1.12 beta BIOS so far?
 

chn

New Member
Dec 22, 2019
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I haven't yet, it seems pretty stable so far, but I have only been running it for a day now.

I was hoping it would add some compatibility to the Samsung LR-DIMMs that I have, but unfortunately they still do not work with this board. So I have reverted to Crucial RDIMMs for now.
 

Janga

New Member
Sep 21, 2019
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I was hoping it would add some compatibility to the Samsung LR-DIMMs that I have, but unfortunately they still do not work with this board. So I have reverted to Crucial RDIMMs for now.
I went down the same road, trying LR-DIMMs and they didn't work. So I ordered the Crucial compatible memory and been great so far. I have two of these boards, each with 256GB RAM (4x 64GB sticks).
 

Evan

Well-Known Member
Jan 6, 2016
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How is the general feeling from the platform now ? Is the system stable and shall we say feature complete ?
 

Iwanovich

New Member
Apr 19, 2020
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2 months later and they still haven't released the BIOS yet. Got the system for extremely cheap but didn't expect it to be such a neglected product.
Well, I bought three of them for about €900,- each. I think it's ridiculous they haven't released a BIOS/UEFI update for more than six months while they are not delivering the product as advertised (16 threads). I'm happy with the beta version @Janga posted, but there are more bugs. I bought these boards to use in an oVirt cluster for my home lab and use GPU/PCIe Passthrough, which I'm unable to because of the "PCI header header 127" bug. This bug has been solved by AMD since AGESA 1.0.0.4b, for which other board vendors released updates since november 2019.
It's time for Asrock Rack to step up their game.
 

Iwanovich

New Member
Apr 19, 2020
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How is the general feeling from the platform now ? Is the system stable and shall we say feature complete ?
In General I'm quite happy with it. I've installed them in some very small cases without any airflow. Putting a Noctua Fan on the CPU heatsink keeps the CPU cool enough and I didn't experience any crashes running them 24/7 for months. One thing to be aware of is the temperature of the X550 chip. Asrock used a small heatsink that easily reaches boiling point when used in a small enclosure without airflow. Putting a 4x4 centimeter fan on top is mandatory in such a scenario.
 

chn

New Member
Dec 22, 2019
13
6
3
How is the general feeling from the platform now ? Is the system stable and shall we say feature complete ?
Besides the lack of support for the LR-DIMMs, I am pretty happy with this board. It's been very stable on the L1.12 BIOS posted in this thread. I would reconsider gettting another ASRock Rack board in future though, based on the support I got - I hear things are better with Supermicro.
 

Aquatechie

Member
Oct 29, 2015
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Nearly 6 months later, ASRock is still shipping the board with the missing threads bug. BIOS L1.12 is still not posted to their website. Many thanks to @Janga for making the beta firmware available to the public!
 

Ed McGuigan

New Member
May 31, 2020
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I have the equivalent Supermicro motherboard and it has been fine. No issue with not seeing the 16vCPUs.