CPU hotplug not working..

Jun 28, 2019
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Hi,

I enabled NUMA on guest hardware, but when try to increase vCPU count, the guest cpu not change..

Memory hotplug is working great!! just CPU is not!!

In the proxmox GUI when I increase the CPU count, the hardware tab stay in RED... and only disappear after a VM shutdown..

Why the CPU stays RED and only increase the guest after a shutdown/reboot? and memory works fine online?
 

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do you have enable cpu hotplug in options ? (like memory hotplug)

if it's a linux vm, which kernel version ? (it should works fine since kernel 4.7)

Note that you can't change socket/cores , but only vcpu option in cpu advanced option

(socket*cores are the max cores you can able, vcpus number is enable/disable theses cores)
 
yes, cpu hotplug and memory is enabled in OPTIONS..

This guest is a Centos7 with Kernel 3.10.XX, which I believe is supported for HOTPLUG!!!

Thanks for the explanation regarding the sockets/cores vs vcpus..

I was trying to online add sockets/cores, not vCPUS... this is working now!!! many thanks!

What is the meaning of have the sockets/cores option in the hardware tab if what really matters is the vCPU count?
 
What is the meaning of have the sockets/cores option in the hardware tab if what really matters is the vCPU count?
Technically, if you have 2 socket x 2 core, or 4socket x 1cores, you'll have 4vcpus, so 4 threads in qemu.

It can be usefull to declare same number of vsocket than your physical machine, if you enable the numa option. (it'll try to map memory/socket/cores of your vm to your physical host)
 
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It can be usefull to declare same number of vsocket than your physical machine, if you enable the numa option. (it'll try to map memory/socket/cores of your vm to your physical host)

Thanks, based on this, what is the best practices? map to guest the same vCPU count as specified in the physical socket/cores tab or it doesn't matters?
 
Thanks, based on this, what is the best practices? map to guest the same vCPU count as specified in the physical socket/cores tab or it doesn't matters?
It doesnt matter.
maybe if you use numa, try to have same number of sockets in your vm.
 
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