linux-kernel - Re: [PATCH RFC 0/3] Add guest cpu

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Date:	Mon, 27 Aug 2012 16:53:56 -0500
From:	Michael Wolf <mjw@...ux.vnet.ibm.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	Avi Kivity <avi@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, peterz@...radead.org, mtosatti@...hat.com,
	mingo@...hat.com
Subject: Re: [PATCH RFC 0/3] Add guest cpu_entitlement reporting

On Mon, 2012-08-27 at 14:41 -0700, Glauber Costa wrote:
> On 08/27/2012 02:27 PM, Michael Wolf wrote:
> > On Mon, 2012-08-27 at 13:31 -0700, Avi Kivity wrote:
> >> On 08/27/2012 01:23 PM, Michael Wolf wrote:
> >>>>
> >>>> How would a guest know what its entitlement is?
> >>>>
> >>>>
> >>>
> >>> Currently the Admin/management tool setting up the guests will put it on
> >>> the qemu commandline.  From this it is passed via an ioctl to the host.
> >>> The guest will get the value from the host via a hypercall.
> >>>
> >>> In the future the host could try and do some of it automatically in some
> >>> cases. 
> >>
> >> Seems to me it's a meaningless value for the guest.  Suppose it is
> >> migrated to a host that is more powerful, and as a result its relative
> >> entitlement is reduced.  The value needs to be adjusted.
> > 
> > This is why I chose to manage the value from the sysctl interface rather
> > than just have it stored as a value in /proc.  Whatever tool was used to
> > migrate the vm could hopefully adjust the sysctl value on the guest.
> >>
> >> This is best taken care of from the host side.
> > 
> > Not sure what you are getting at here.  If you are running in a cloud
> > environment, you purchase a VM with the understanding that you are
> > getting certain resources.  As this type of user I don't believe you
> > have any access to the host to see this type of information.  So the
> > user still wouldnt have a way to confirm that they are receiving what
> > they should be in the way of processor resources.
> > 
> > Would you please elaborate a little more on this?
> 
> What do you mean they have no access to the host?
> They have access to all sorts of tools that display information from the
> host. Speaking of a view-only resource, those are strictly equivalent.
> 
> 
> 

ok.  I will go look at those resources. 

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