Explanation of virtual CPUs in KVM

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#1 Thu, 01/23/2014 - 10:11

pixel_paul

Explanation of virtual CPUs in KVM

Hi,

I've got a hexacore processor and am wanting to split the cores to various VMs. Can someone explain how this works please?

Virtual CPU options
Number of virtual CPUs    1
Number of cores per socket   1
Real CPUs on host system     
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 0
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 1
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 2
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 3
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 4
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 5
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 0
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 1
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 2
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 3
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 4
Intel(R) Xeon(R) CPU E5-2430 0 @ 2.20GHz, IC 0, core 5

Thanks,

Paul

#2 Thu, 01/23/2014 - 14:11

andreychek

Howdy,

Are you asking about why it shows 12 cores?

Those are the cores that the Linux kernel sees... you can see what exactly the Linux kernel thinks is there by viewing /proc/cpuinfo on the host.

I believe your particular CPU has two virtual cores for each physical core, which makes it appear that there are 12 cores in all.

-Eric

#3 Fri, 01/24/2014 - 04:56 (Reply to #2)

pixel_paul

Hi,

No, I understand that. What I am wondering about is how the cores/virtual cores are assigned to the VMs and what that means.

So for example, if I have 6 VMs can I assign 2 virtual cores to each VM? And if so how do I do that using the form?

Thanks,

Paul

#4 Mon, 02/03/2014 - 20:57

scotwnw

Cloudmin / Virtual System Owners / account plans.

Assign 100% cpu for each cores worth of usage. The thing Im not sure of is Intel's virtual cores.... are those 100% each per virtual core and thus 1 physical core is actually 200%. I'd assume so since the kernel sees it as seperate cores. So for intel, 1 physical core worth of use is = 200% cpu.

I use AMD and they dont use that virtual core hocum. So 100% per core on AMD is 100% of 1 physical core.

#5 Wed, 02/05/2014 - 10:53 (Reply to #4)

pixel_paul

Ok, at the moment its set to unlimited, and so hypothetically does this means that if i have 13 virtual servers all running at 100% usage I would be running at 1300%, so over the capacity of the server?

I'm confused!

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