Subject: Re: [PATCH v3 0/3] cpu: pseries: Cpu offline states framework
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Gautham R Shenoy <ego@in.ibm.com>, Joel Schopp <jschopp@austin.ibm.com>,
       Balbir Singh <balbir@in.ibm.com>,
       Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>,
       Dipankar Sarma <dipankar@in.ibm.com>,
       Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
       Arun R Bharadwaj <arun@linux.vnet.ibm.com>,
       linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
       "Darrick J. Wong" <djwong@us.ibm.com>
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References: <20090915120629.20523.79019.stgit@sofia.in.ibm.com>
	 <1253016701.5506.73.camel@laptop>
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Date: Thu, 24 Sep 2009 10:51:41 +1000
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On Tue, 2009-09-15 at 14:11 +0200, Peter Zijlstra wrote:
> I still think its a layering violation... its the hypervisor manager
> that should be bothered in what state an off-lined cpu is in. 
> 
That's not how our hypervisor works.

If you ask through the management interface, to remove a CPU from a
partition, the HV will communicate with a daemon inside the partition
that will then unplug the CPU via the right call.

I don't really understand your objections to be honest. And I fail to
see why it would be a layering violation to have the ability for the OS
to indicate in what state it wishes to relinguish a CPU to the
hypervisor, which more or less defines what is the expected latency for
getting it back later on.

Ben.


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