linux-kernel - Re: [PATCH v3 0/3] cpu: pseries: Cpu offline states framework

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Date:	Thu, 24 Sep 2009 10:51:41 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	"Darrick J. Wong" <djwong@...ibm.com>
Subject: Re: [PATCH v3 0/3] cpu: pseries: Cpu offline states framework

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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