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


From: Alexandre DERUMIER
Subject: Re: [Qemu-devel] [PATCH v2 00/11] cpu: add i386 cpu hot remove support
Date: Mon, 26 Jan 2015 04:25:24 +0100 (CET)

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

About this, it seem to be a display bug in "info numa",
cpu is correctly assigned to numa node1 in the guest.


----- Mail original -----
De: "aderumier" <address@hidden>
À: "Zhu Guihua" <address@hidden>
Cc: "qemu-devel" <address@hidden>, address@hidden, "guz fnst" <address@hidden>, 
"isimatu yasuaki" <address@hidden>, "Anshul Makkar" <address@hidden>, "chen fan 
fnst" <address@hidden>, "Igor Mammedov" <address@hidden>, "afaerber" 
<address@hidden>
Envoyé: Lundi 26 Janvier 2015 04:19:52
Objet: Re: [Qemu-devel] [PATCH v2 00/11] cpu: add i386 cpu hot remove support

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" <address@hidden> 
À: "aderumier" <address@hidden> 
Cc: "qemu-devel" <address@hidden>, address@hidden, "guz fnst" <address@hidden>, 
"isimatu yasuaki" <address@hidden>, "Anshul Makkar" <address@hidden>, "chen fan 
fnst" <address@hidden>, "Igor Mammedov" <address@hidden>, "afaerber" 
<address@hidden> 
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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