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From: Gleb Natapov <gleb@redhat.com>
Subject: Re: cpu hotplug
Date: Sun, 19 Sep 2010 17:41:14 +0200
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Cc: "Kevin O'Connor" <kevin@koconnor.net>, kvm@vger.kernel.org
To: Conrad Wood <linux-kvm@conradwood.net>
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On Sun, Sep 19, 2010 at 05:37:18PM +0200, Conrad Wood wrote:
> 
> > > I need to know if a cpu is currently inserted or ejected.
> > > 
> > The only way to do that currently is to track it in your management app.
> 
> The Management App does know which one should be inserted or ejected.
> I see now way of enforcing it though.
> 
> This is what I had in mind: (simplified)
> 
> 1. Management App increase cpus
> 2. kvm (as instructed by app): insert cpu x
> 3. guest os: online cpu x
> 4. do some stuff in the guest...
> 5. guest os: offline cpu x
> 6. Management App decrease cpus
> 7. kvm (as instructed by app): eject cpu x 
> 
> However after step 7 the guest can turn the cpu online again by issuing 
> echo 1 >/sys/devices/.../cpuX/online
There will be no /sys/devices/.../cpuX/online in guest after step 7.

> If the guest does so, the Management App has no way of knowing and thus
> cannot provide accurate logs - that is why it is so important.
> 
> Conrad
> 
> 

--
			Gleb.