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VM / vCPU and usage

  • 24 December 2021
  • 1 reply
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L

Hi there,

I need explaination about vCPU usage :

  • My CPU Model is Intel(R) Xeon(R) Silver 4208 CPU @ 2.10GHz (8 core, 16 thread) 
  • I have two socket per host
  • So 2 x 8 = 16 cores and 4200 Mhz (base freq) / 6400 Mhz (max turbo freq)
  • So 32 vCPU (16 cores x 2 = 32 thread with Hyperthreading)
  • A VM use 6 vCPU and 1 core
  • Prism report for this VM, 97% of CPU usage

97% of what ? Is that 6400 / 32 x 6 = 1200 Mhz ?? The half a physical CPU ?

How that calculation is made ?

Thanks,

Jerome

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Best answer by DavidN 3 January 2022, 16:19

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DavidN
Userlevel 3
Badge +6

Hi @llopht

Great question… got me interested in looking up a few things. While it would have been helpful to know which hypervisor and AOS version you’re running, I’ll include what I found for AHV and ESXi. (I assume AHV since you didn’t mention Hyper-V nor vCenter).

Ultimately I think this KB should answer your question (but not directly from Prism). I’d be curious to see which value Prism shows in your scenario.

No Intel Turbo Boost frequencies shown in the output of "cpupower frequency-info" command on AHV host

In short summary use the following AHV commands to find out the CPU frequency values:

cpupower frequency-info
sudo turbostat

Throw in an “lscpu | more” for good measure and you should have sufficient info to find out what the VM is using. Interestingly enough, on AHV you’d also would need to check if the BIOS (see KB) to confirm if CPU settings were indeed set enabled.

For VMware see KB 80610 for a similar description/cpu info.

EDIT:

Wanted to mention a related Nutanix KB article which presents an interesting twist in situations where a power supply is out. 

Degraded CPU performance on hosts due to lack of power supply redundancy

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