Virtualization: CPU and memory hotplug

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Linux kernel supports cpu-hotplug mechanism. You can enable or disable CPU without a system reboot. CPU hotplug is not just useful to replace defective components it can also be applied in other contexts to increase the productivity of a system. For example on a single system running multiple Linux partitions, as the workloads change it would be extremely useful to be able to move CPUs from one partition to the next as required without rebooting or interrupting the workloads.

 

Is this feature useful in a Virtualization setting?   Should KVM support CPU and memory hotplug?    Are there some customer who say, well, doesn't matter if this feature exists, I don't trust hotplug, I will restart my VMs to ensure data integrity?

 

I need your help to figure out the timing for supporting this, RHEL7 timeframe or earlier?

Responses

I think that both CPU and memory hotplug are useful and would definitely take advantage of the functionality with KVM if it were made available. VMware has provided this functionality with RHEL since 5.4 (I believe?), but only on VT-enabled 64-bit VMs.

This was one of the major advantages of Solaris on Sparc hardware--I used to use Solaris Dynamic Reconfiguration extensively at a university I worked for and it helped to maintain high availability by permitting capacity adds/removes without the overhead of scheduled maintenance.

In a big organization I think that this possibility is really needed. Today for us is really a pain to restart the guest to add memory and cpu.

In my opinion is a Must Have

Whilst not essential - this would definitely be a "good to have feature".  There are other "must have" virtualization features that need development though.

It's already supported! CPU since RHEV 3.4 and memory since RHEV 3.6

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