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

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Date:	Wed, 16 Sep 2009 20:58:20 +0530
From:	Dipankar Sarma <dipankar@...ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Balbir Singh <balbir@...ibm.com>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.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, Sep 15, 2009 at 02:11:41PM +0200, Peter Zijlstra wrote:
> On Tue, 2009-09-15 at 17:36 +0530, Gautham R Shenoy wrote:
> > This patchset contains the offline state driver implemented for
> > pSeries. For pSeries, we define three available_hotplug_states. They are:
> > 
> >         online: The processor is online.
> > 
> >         offline: This is the the default behaviour when the cpu is offlined
> > 
> >         inactive: This cedes the vCPU to the hypervisor with a cede latency
> > 
> > Any feedback on the patchset will be immensely valuable.
> 
> I still think its a layering violation... its the hypervisor manager
> that should be bothered in what state an off-lined cpu is in. 

The problem is that all hypervisor managers cannot figure out what sort
of latency guest OS can tolerate under the situation. They wouldn't know
from what context guest OS has ceded the vcpu. It has to have
some sort of hint, which is what the guest OS provides.

Thanks
Dipankar
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