[pve-devel] qemu2.7: cpu hotplug && hot-unplug v1

[Alexandre DERUMIER]

>>small question to live migration, you wrote the hot plug features breaks 
>>live migration but the qemu wiki says that this should work. 

The wiki is pretty old.
When I said that it break live migration,It's only if you have already enable livemigration on qemu 2.6 and try to migrate to new qemu 2.7 hotplug system.

I only applied the new hotplug system when the vm is stop/start a first time (to have 2.7 machine version running).

So this does not break the migration.


Here the last doc for cpu hotplug (the doc is not yet commited in qemu git)
https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg03157.html

----- Mail original -----
De: "Harald Leithner" <leithner at itronic.at>
À: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Mercredi 7 Septembre 2016 09:26:57
Objet: Re: [pve-devel] qemu2.7: cpu hotplug && hot-unplug v1

Hi, 

small question to live migration, you wrote the hot plug features breaks 
live migration but the qemu wiki says that this should work. 
The only limitations are: 

1. migration target should be started with initial CPU count '-smp XX' 
that includes hot-added CPUs on migration source side. 
2. CPU shouldn't be hot-plugged during migration. 
adding CPUs should be done in successive order from lower to higher IDs 
3. in [0..max-cpus) range. 
It's possible to add arbitrary CPUs in random order, however that would 
cause migration to fail on its target side. 

http://wiki.qemu.org/Features/CPUHotplug 

Or is only the implementation for proxmox limited? 

Harald 

Am 06.09.2016 um 12:41 schrieb Alexandre Derumier: 
> Hi, 
> This patch series implement new qemu 2.7 cpu hotplug framework, with device_add|device_del 
> 
> hot-unplug is working now ! 
> 
> config example: 
> --------------- 
> cpu: kvm64 
> sockets:2 
> cores:2 
> 
> generate cmdline 
> ---------------- 
> -cpu kvm64,+lahf_lm,+sep,+kvm_pv_unhalt,+kvm_pv_eoi,enforce 
> -smp 1,sockets=2,cores=2,maxcpus=4 
> -device kvm64-x86_64-cpu,id=cpu2,socket-id=0,core-id=1,thread-id=0 
> -device kvm64-x86_64-cpu,id=cpu3,socket-id=1,core-id=0,thread-id=0 
> -device kvm64-x86_64-cpu,id=cpu4,socket-id=1,core-id=1,thread-id=0 
> 
> 
> First core is not hotpluggable (-smp 1). (socket-id=0,core-id=0) 
> Others cores are added with -device, with cpumodel,socket-id && core-id. 
> 
> cpuflags are defined globally in -cpu , and are auto applied on hotplug 
> 
> Tested with debian jessie, kernel 3.16. 
> 
> This new config is only apply with machine 2.7+cpu hotplug enabled, as it break live migration. 
> 
> 
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> 

-- 
Harald Leithner 

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