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

Marcelo Tosatti
2013-03-06T01:59:00Z

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?

Probably don't need to report new data to the guest for that.