Re: [Qemu-devel] [PATCH v2 00/11] cpu: add i386 cpu hot remove support

[Alexandre DERUMIER <aderumier@odiso.com>]

Thanks for your reply.

2 others things:

1)
on cpu unplug, I see that the cpu is correctly removed from my linux guest but not from qemu

starting with a guest with 3cpus:

guest: #ls -lah /sys/devices/system/ |grep cpu
drwxr-xr-x 6 root root    0 Jan 25 22:16 cpu0
drwxr-xr-x 6 root root    0 Jan 25 22:16 cpu1
drwxr-xr-x 6 root root    0 Jan 25 22:16 cpu2

hmp: # info cpus
* CPU #0: pc=0xffffffff81057022 (halted) thread_id=24972
  CPU #1: pc=0xffffffff81057022 (halted) thread_id=24973
  CPU #2: pc=0xffffffff81048bc1 (halted) thread_id=25102


then unplug cpu2
hmp : device_del cpu2

guest:

dmesg:
[  176.219754] Unregister pv shared memory for cpu 2
[  176.278881] smpboot: CPU 2 is now offline

#ls -lah /sys/devices/system/ |grep cpu
drwxr-xr-x 6 root root    0 Jan 25 22:16 cpu0
drwxr-xr-x 6 root root    0 Jan 25 22:16 cpu1

hmp: # info cpus
* CPU #0: pc=0xffffffff81057022 (halted) thread_id=24972
  CPU #1: pc=0xffffffff81057022 (halted) thread_id=24973
  CPU #2: pc=0xffffffff81048bc1 (halted) thread_id=25102




2)when numa is used, the hotplugged cpu is always on numa node 0
  (cpu_add or device_add cpu)


starting a guest, with 2 sockets,1 cores

-smp 2,sockets=2,cores=1,maxcpus=2
-object memory-backend-ram,size=256M,id=ram-node0 -numa node,nodeid=0,cpus=0,memdev=ram-node0 
-object memory-backend-ram,size=256M,id=ram-node1 -numa node,nodeid=1,cpus=1,memdev=ram-node1 

hmp:
# info numa
2 nodes
node 0 cpus: 0
node 0 size: 256 MB
node 1 cpus: 1
node 1 size: 256 MB

ok

now

starting with same topology, but with 1cpu at start
-smp 2,sockets=2,cores=1,maxcpus=2
-object memory-backend-ram,size=256M,id=ram-node0 -numa node,nodeid=0,cpus=0,memdev=ram-node0 
-object memory-backend-ram,size=256M,id=ram-node1 -numa node,nodeid=1,cpus=1,memdev=ram-node1 

# info numa
2 nodes
node 0 cpus: 0
node 0 size: 256 MB
node 1 cpus: 
node 1 size: 256 MB

hotpluging a cpu
# device_add kvm64-x86_64-cpu,apic-id=1,id=cpu1

# info numa
2 nodes
node 0 cpus: 0 1
node 0 size: 256 MB
node 1 cpus: 
node 1 size: 256 MB

cpu1 should be on node1, not node0.


Regards,

Alexandre

----- Mail original -----
De: "Zhu Guihua" <zhugh.fnst@cn.fujitsu.com>
À: "aderumier" <aderumier@odiso.com>
Cc: "qemu-devel" <qemu-devel@nongnu.org>, tangchen@cn.fujitsu.com, "guz fnst" <guz.fnst@cn.fujitsu.com>, "isimatu yasuaki" <isimatu.yasuaki@jp.fujitsu.com>, "Anshul Makkar" <anshul.makkar@profitbricks.com>, "chen fan fnst" <chen.fan.fnst@cn.fujitsu.com>, "Igor Mammedov" <imammedo@redhat.com>, "afaerber" <afaerber@suse.de>
Envoyé: Lundi 26 Janvier 2015 03:01:48
Objet: Re: [Qemu-devel] [PATCH v2 00/11] cpu: add i386 cpu hot remove support

On Fri, 2015-01-23 at 11:24 +0100, Alexandre DERUMIER wrote: 
> Hello, 
> 
> I'm currently testing the new cpu unplug features, 
> Works fine here with debian guests and kernel 3.14. 
> 

Thanks for your test. 

> But I have notice some small potential bugs, but I'm not sure I'm doing it right. 
> 
> 1)first, to unplug cpu, we need an id for cpu 
> 

Yes, if you want to unplug cpu, you must have an id for cpu. 

> The problem is that the current qemu command line 
> -smp 1,sockets=2,cores=1,maxcpus=2 
> 
> for example, will create 1 cpu on apic-id 0 without any id, so we can't unplug it. 
> 
> 
> So, I have tried with 
> 
> -smp 1,sockets=2,cores=1,maxcpus=2 -device kvm64-x86_64-cpu,apic-id=0,id=cpu0 
> 
> But this give me an error: 
> "-device kvm64-x86_64-cpu,apic-id=0,id=cpu0: CPU with APIC ID 0 exists" 
> 

APIC ID 0 was used by the cpu of '-smp 1'. 
So you should use apic-id=1 

> (also try to set -smp 0, but it's not working). 
> 
> 
> 
> 2) second problem, if I start with 
> -smp 1,sockets=2,cores=1,maxcpus=2 
> 
> then hmp: 
> device_add kvm64-x86_64-cpu,apic-id=1,id=cpu1 
> 
> then hmp : device_del cpu1 
> 
> Got an error:" 
> This is the last cpu, should not be removed!" 
> 
> 

Oh, it's our problem, thanks for your pointing out. 
I will fix it in next version. 

Regards, 
Zhu 

> 
> This is coming from 
> [PATCH 06/12] pc: add cpu hot unplug request callback support 
> + if (smp_cpus == 1) { 
> + error_setg(&local_err, 
> + "This is the last cpu, should not be removed!"); 
> + goto out; 
> + } 
> 
> 
> 
> So, the only way unplug is working for me, is to start with -smp 2 minimum 
> -smp 2,sockets=2,cores=1,maxcpus=4 
> 
> Then I can hotplug|unplug cpuid >= 2 
> 
> 
> 
> Regards, 
> 
> Alexandre Derumier 
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