linux-kernel - Re: [PATCH 0/4] Alter steal-time reporting in the guest

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Date:	Wed, 06 Mar 2013 10:27:13 -0600
From:	Michael Wolf <mjw@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org, riel@...hat.com, gleb@...hat.com,
	kvm@...r.kernel.org, peterz@...radead.org, glommer@...allels.com,
	mingo@...hat.com, anthony@...emonkey.ws
Subject: Re: [PATCH 0/4] Alter steal-time reporting in the guest

On Tue, 2013-03-05 at 22:41 -0300, Marcelo Tosatti wrote:
> On Tue, Mar 05, 2013 at 02:22:08PM -0600, Michael Wolf wrote:
> > Sorry for the delay in the response.  I did not see the email
> > right away.
> > 
> > On Mon, 2013-02-18 at 22:11 -0300, Marcelo Tosatti wrote:
> > > On Mon, Feb 18, 2013 at 05:43:47PM +0100, Frederic Weisbecker wrote:
> > > > 2013/2/5 Michael Wolf <mjw@...ux.vnet.ibm.com>:
> > > > > In the case of where you have a system that is running in a
> > > > > capped or overcommitted environment the user may see steal time
> > > > > being reported in accounting tools such as top or vmstat.  This can
> > > > > cause confusion for the end user.
> > > > 
> > > > Sorry, I'm no expert in this area. But I don't really understand what
> > > > is confusing for the end user here.
> > > 
> > > I suppose that what is wanted is to subtract stolen time due to 'known
> > > reasons' from steal time reporting. 'Known reasons' being, for example,
> > > hard caps. So a vcpu executing instructions with no halt, but limited to
> > > 80% of available bandwidth, would not have 20% of stolen time reported.
> > 
> > Yes exactly and the end user many times did not set up the guest and is
> > not aware of the capping.  The end user is only aware of the performance
> > level that they were told they would get with the guest.  
> > > But yes, a description of the scenario that is being dealt with, with
> > > details, is important.
> > 
> > I will add more detail to the description next time I submit the
> > patches.  How about something like,"In a cloud environment the user of a
> > kvm guest is not aware of the underlying hardware or how many other
> > guests are running on it.  The end user is only aware of a level of
> > performance that they should see."   or does that just muddy the picture
> > more??
> 
> So the feature aims for is to report stolen time relative to hard
> capping. That is: stolen time should be counted as time stolen from
> the guest _beyond_ hard capping. Yes?
Yes, that is the goal.
> 
> Probably don't need to report new data to the guest for that.
Not sure I understand what you are saying here. Do you mean that I don't
need to report the expected steal from the guest?  If I don't do that
then I'm not reporting all of the time and changing /proc/stat in a
bigger way than adding another catagory.  Also I thought I would need to
provide the consigned time and the steal time for debugging purposes.
Maybe I'm missing your point.....
> 
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