Arch Linux

jojo06

Member

Registered: 2023-11-04

Posts: 373

[SOLVED]Why is QEMU/Kvm detecting less cpu than vbox?

VirtualBox shows 12 CPUs on my computer. The `lscpu` output shows 6. But I wonder if the fact that QEMU/Kvm is much faster is because it runs cores and threads with the vCPU system and speeds it up with virtualization? That's why I wonder if it has 6.

I did the virtualization from the wiki and when I checked, the hardware is suitable for it. No 9p yet, modprobe added. Could the problem be the `108` in the groups output? I had vboxusers, when I uninstalled virtualbox and deleted the user from group it replaced 108. Could it be that somehow vbox is still using the cpu?

lsmod | grep kvm

kvm_intel             425984  0
kvm                  1376256  1 kvm_intel
irqbypass              12288  1 kvm

Last edited by jojo06 (2023-12-05 15:25:31)

twelveeighty

Member

Registered: 2011-09-04

Posts: 1,451

Re: [SOLVED]Why is QEMU/Kvm detecting less cpu than vbox?

Post the full output of 'lscpu'.

jojo06

Member

Registered: 2023-11-04

Posts: 373

Re: [SOLVED]Why is QEMU/Kvm detecting less cpu than vbox?

lscpu

Architecture:            x86_64
  CPU op-mode(s):        32-bit, 64-bit
  Address sizes:         39 bits physical, 48 bits virtual
  Byte Order:            Little Endian
CPU(s):                  6
  On-line CPU(s) list:   0-5
Vendor ID:               GenuineIntel
  Model name:            Intel(R) Core(TM) i5-9400F CPU @ 2.90GHz
    CPU family:          6
    Model:               158
    Thread(s) per core:  1
    Core(s) per socket:  6
    Socket(s):           1
    Stepping:            10
    CPU(s) scaling MHz:  40%
    CPU max MHz:         4100.0000
    CPU min MHz:         800.0000
    BogoMIPS:            5802.42
    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 art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni pclm
                         ulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb pti ssbd ibrs ibpb stibp tpr_shadow flexpriority ept 
                         vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid mpx rdseed adx smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp vnmi md_clear flush_l1d arch_capabilities
Virtualization features: 
  Virtualization:        VT-x
Caches (sum of all):     
  L1d:                   192 KiB (6 instances)
  L1i:                   192 KiB (6 instances)
  L2:                    1.5 MiB (6 instances)
  L3:                    9 MiB (1 instance)
NUMA:                    
  NUMA node(s):          1
  NUMA node0 CPU(s):     0-5
Vulnerabilities:         
  Gather data sampling:  Mitigation; Microcode
  Itlb multihit:         KVM: Mitigation: VMX disabled
  L1tf:                  Mitigation; PTE Inversion; VMX conditional cache flushes, SMT disabled
  Mds:                   Mitigation; Clear CPU buffers; SMT disabled
  Meltdown:              Mitigation; PTI
  Mmio stale data:       Mitigation; Clear CPU buffers; SMT disabled
  Retbleed:              Mitigation; IBRS
  Spec rstack overflow:  Not affected
  Spec store bypass:     Mitigation; Speculative Store Bypass disabled via prctl
  Spectre v1:            Mitigation; usercopy/swapgs barriers and __user pointer sanitization
  Spectre v2:            Mitigation; IBRS, IBPB conditional, STIBP disabled, RSB filling, PBRSB-eIBRS Not affected
  Srbds:                 Mitigation; Microcode
  Tsx async abort:       Not affected

Thank you for your interest

spiffeeroo

Member

Registered: 2021-04-23

Posts: 23

Re: [SOLVED]Why is QEMU/Kvm detecting less cpu than vbox?

Intel i5 9400F is a 6 core/6 thread CPU. There is no Hyperthreading/SMT on that CPU.

jojo06

Member

Registered: 2023-11-04

Posts: 373

Re: [SOLVED]Why is QEMU/Kvm detecting less cpu than vbox?

Intel i5 9400F is a 6 core/6 thread CPU. There is no Hyperthreading/SMT on that CPU.

I understand, but will the guest work comfortably with 2 vCPUs? Will Arch have problems/slowness if I set 3 or 4?

twelveeighty

Member

Registered: 2011-09-04

Posts: 1,451

Re: [SOLVED]Why is QEMU/Kvm detecting less cpu than vbox?

There's only one way to find out. It's impossible to predict, since it depends on what the guest and host are doing at the same time.