htop and sytem-monitor shows 0 cpu ubuntu 20.04 ryzen 3950x

Question

I freshly built a new PC and make dual boot with an Ubuntu 20.04. Im having trouble with ryzen 3950x, htop and system monitor didn't recognize cpu (instead of 32 shows 1 thread). I must start it with acpi=off because ubuntu wont starts. Is it a problem with compatibility? My BIOS was updated at the time of building the pc (3 weeks ago, B550 AORUS ELITE AX V2 (rev. 1.0)) Can you help me with wrong number of threads in htop/system monitor

Im confused

(base) B550-AORUS-ELITE-AX-V2:~$ cat /proc/cpuinfo
processor   : 0
vendor_id   : AuthenticAMD
cpu family  : 23
model       : 113
model name  : AMD Ryzen 9 3950X 16-Core Processor
stepping    : 0
microcode   : 0x8701021
cpu MHz     : 3606.771
cache size  : 512 KB
physical id : 0
siblings    : 1
core id     : 0
cpu cores   : 1
apicid      : 0
initial apicid  : 0
fpu     : yes
fpu_exception   : yes
cpuid level : 16
wp      : yes
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 ibs skinit wdt tce topoext perfctr_core perfctr_nb bpext perfctr_llc mwaitx cpb cat_l3 cdp_l3 hw_pstate sme ssbd mba sev ibpb stibp vmmcall fsgsbase bmi1 avx2 smep bmi2 cqm rdt_a rdseed adx smap clflushopt clwb sha_ni xsaveopt xsavec xgetbv1 xsaves cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local clzero irperf xsaveerptr wbnoinvd arat npt lbrv svm_lock nrip_save tsc_scale vmcb_clean flushbyasid decodeassists pausefilter pfthreshold avic v_vmsave_vmload vgif umip rdpid overflow_recov succor smca
bugs        : sysret_ss_attrs spectre_v1 spectre_v2 spec_store_bypass
bogomips    : 6986.68
TLB size    : 3072 4K pages
clflush size    : 64
cache_alignment : 64
address sizes   : 43 bits physical, 48 bits virtual
power management: ts ttp tm hwpstate cpb eff_freq_ro [13] [14]

(base) B550-AORUS-ELITE-AX-V2:~$ sudo dmidecode -t 4 | egrep -i 'core (count|enabled)|thread count|Version'
    Version: AMD Ryzen 9 3950X 16-Core Processor            
    Core Count: 16
    Core Enabled: 16
    Thread Count: 32

(base) B550-AORUS-ELITE-AX-V2:~$ sudo dmidecode -s bios-version
[sudo] password: 
F10
(base) B550-AORUS-ELITE-AX-V2:~$ free -h
              total        used        free      shared  buff/cache   available
Mem:           62Gi       1,9Gi        59Gi       131Mi       1,8Gi        60Gi
Swap:          15Gi          0B        15Gi
(base) B550-AORUS-ELITE-AX-V2:~$ sudo lshw -C memory
  *-firmware                
       description: BIOS
       vendor: American Megatrends Inc.
       physical id: 0
       version: F10
       date: 09/18/2020
       size: 64KiB
       capacity: 32MiB
       capabilities: pci upgrade shadowing cdboot bootselect socketedrom edd int13floppy1200 int13floppy720 int13floppy2880 int5printscreen int14serial int17printer acpi usb biosbootspecification uefi
  *-memory
       description: System Memory
       physical id: 9
       slot: System board or motherboard
       size: 64GiB
     *-bank:0
          description: DIMM DDR4 Synchronous Unbuffered (Unregistered) 2133 MHz (0,5 ns)
          product: F4-3200C16-16GIS
          vendor: Unknown
          physical id: 0
          serial: 00000000
          slot: DIMM 0
          size: 16GiB
          width: 64 bits
          clock: 2133MHz (0.5ns)
     *-bank:1
          description: DIMM DDR4 Synchronous Unbuffered (Unregistered) 2133 MHz (0,5 ns)
          product: F4-3200C16-16GIS
          vendor: Unknown
          physical id: 1
          serial: 00000000
          slot: DIMM 1
          size: 16GiB
          width: 64 bits
          clock: 2133MHz (0.5ns)
     *-bank:2
          description: DIMM DDR4 Synchronous Unbuffered (Unregistered) 2133 MHz (0,5 ns)
          product: F4-3200C16-16GIS
          vendor: Unknown
          physical id: 2
          serial: 00000000
          slot: DIMM 0
          size: 16GiB
          width: 64 bits
          clock: 2133MHz (0.5ns)
     *-bank:3
          description: DIMM DDR4 Synchronous Unbuffered (Unregistered) 2133 MHz (0,5 ns)
          product: F4-3200C16-16GIS
          vendor: Unknown
          physical id: 3
          serial: 00000000
          slot: DIMM 1
          size: 16GiB
          width: 64 bits
          clock: 2133MHz (0.5ns)
  *-cache:0
       description: L1 cache
       physical id: c
       slot: L1 - Cache
       size: 1MiB
       capacity: 1MiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
       configuration: level=1
  *-cache:1
       description: L2 cache
       physical id: d
       slot: L2 - Cache
       size: 8MiB
       capacity: 8MiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
       configuration: level=2
  *-cache:2
       description: L3 cache
       physical id: e
       slot: L3 - Cache
       size: 64MiB
       capacity: 64MiB
       clock: 1GHz (1.0ns)
       capabilities: pipeline-burst internal write-back unified
       configuration: level=3
(base) B550-AORUS-ELITE-AX-V2:~$ 

Answer 1

ACPI

acpi=off will break a lot of things. Any specifics on why this is necessary?

Although it's kind of old, you might look at this.

Is your CPU overclocked, or memory XMP enabled?

Also, try Ubuntu 20.10 and see if it works without acpi=off.

BIOS

B550 AORUS ELITE AX V2 (rev. 1.0)

You have BIOS version F10.

There's a newer BIOS available, version F11d, dated 10/29/2020, and can be downloaded here.

Note: Confirm that I have the correct web page for your motherboard model #.

Note: Have good backups before updating the BIOS.

memory

AMD Ryzen 9 3950X 16-Core Processor

Ryzen processors are notorious for memory compatibility issues.

Look at the CPU Support List to determine your CPU family). (Matisse)

Look at the Memory Support List and download the Matisse .pdf to confirm that your memory is listed.

Go to https://www.memtest86.com/ and download/run their free memtest to test your memory. Get at least one complete pass of all the 4/4 tests to confirm good memory. This WILL take many hours to complete on 64G.