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

Michael Wolf
2013-03-06T16:28:44Z

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@linux.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.....
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>