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

Michael Wolf
2013-03-06T16:34:41Z

On Wed, 2013-03-06 at 14:34 +0100, Frederic Weisbecker wrote:
> 2013/3/5 Michael Wolf <mjw@linux.vnet.ibm.com>:
> > 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??
>
> That alone is probably not enough. But yeah, make sure you clearly
> state the difference between expected (caps, sched bandwidth...) and
> unexpected (overcommitting, competing load...) stolen time. Then add a
> practical example as you made above that explains why it matters to
> make that distinction and why you want to report it.
>

Ok, I understand what you are requesting. I will make sure to add it to
the description the next time I submit the patches.