CPU Reservations

[elis2019]

Hello All,

My apologies if the question below is already answered, I couldn't seem to find an answer for this.

So our machine (built on Cent OS) is installed and managed by out third party in their VMware Infrastructure. We have our requirement that the CPU cores need to be reserved, I understand the fact that the CPU reservation in VMWare is done based on the CPU clock cycles (in Mhz). The vendor has reserved 2000 Mhz for our machine which I believe is just 1 core (The cycle speed for each core is 2000 MHz) so I assume, its 1 core thats been "reserved". Is there a way for me to check the average used CPU clock cycles used by our Cent OS machine over a period of time so that we can ask the vendor to modify the "reserved" clock cycles?

[Teddy092]

Hi elis2019,

To do so, you can access the vCenter that manages the whole infrastructure If not, you may request to your provider a read only access to your VMs is possible.

Once you're good with the access, within vCenter you can go to the "Monitor" tab after selecting your VM, then under "Performance" > "Overview", you select the period of time you're interested in from the drop down menu and you'll have for example like in the screenshot below the CPU usage within the last week.

[elis2019]

Hello,

Thank you for the email, it helps. Just to confirm that the CPU reservation is done based on the cpu cycles and not CPU cores. My understanding is

E.g. An ESX with  4 core CPU with 1.9 GHz cycle will have 8GHz  (2 GHz pr core) or 8000 MHz in total and when I installed a guest in this ESX, if I assign the Reservation value to 6000 MHz, it means I'm allocating 3 cores of CPU. Is that right?

[Teddy092]

Hi elis2019,

Yes your understanding in this example here is right. For a CPU of 4 cores running at 2Ghz, the total CPU capacity of the ESXi will be 8Ghz.

However when you reserve a certain CPU capacity for a VM, it doesn't necessarily mean that you allocate like in your example here 3 cores of the host CPU.

Please check the VMware docs below that may help you better understand how this works.

Configuring Multicore Virtual CPUs

Virtual CPU Configuration

Hope that helps :smileyhappy:

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