Re: [PATCH] cpu hotplug issue

Vasilis Liaskovitis
2011-07-27T16:35:30Z

Hi,

On Mon, Jul 25, 2011 at 3:18 PM, Jan Kiszka <jan.kiszka@siemens.com> wrote:
>
> OK, hacks below plus the following three patches make CPU hotplug work
> again - with some exceptions. Here are the patches:
>
> 1. http://thread.gmane.org/gmane.comp.emulators.kvm.devel/76484
> 2. http://thread.gmane.org/gmane.comp.emulators.qemu/110272
> 3. http://thread.gmane.org/gmane.comp.emulators.qemu/110426
>
> And here are the hacks (well, the first hunk is clearly a fix, the last
> one clearly a hack, /me still undecided about the rest):

thanks for these. Testing a bit late here...
Applying these 3 patches + hacks/fix on master doesn't solve the
initial "CPU: not responding" dmesg hotplug issue on my setup.
The ACPI event is delivered correctly, but "echo 1 >
/sys/devices/system/cpu/cpuX/online" still fails.
e.g. tested with "-smp 1,maxcpus=2"

Could you share your qemu-kvm command line? I have been trying 2.6.39
guest kernel (as opposed to 3.0.2) but
I doubt that's the issue.
Can someone else confirm whether this solves the issue for their setup or not?

> I see two remaining problems:
> - kvmclock is somehow broken, either in my guest kernel (OpenSUSE HEAD
> 3.0.0-2) or the host, -cpu host,-kvmclock works around sporadic
> guest lockups on echo 1 > /sys...

could you explain this a bit further? specifying "-cpu host,-kvmclock"
avoids the lockups? I have tried
adding this to my command line but didn't help (but then again my
problem is not guest lockups: the onlining fails)

> - Seabios tends to lock up once every few system_reset after some
> CPU has been hot-added - also in TCG mode. It seems to dislike any
> setup of #CPUs > smp_cpus (whatever that implies in details).

I always get a lockedup seabios when rebooting after a hotplug attempt
with these patches (or with my initial vcpu_dirty workaround FWIW)

thanks,

- Vasilis