linux-kernel - Re: [PATCH RFC V2 0/5] Separate consigned (expected steal) from steal time.

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Message-ID: <1350486837.6414.3.camel@lambeau>
Date:	Wed, 17 Oct 2012 10:13:57 -0500
From:	Michael Wolf <mjw@...ux.vnet.ibm.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	peterz@...radead.org, mtosatti@...hat.com, mingo@...hat.com,
	avi@...hat.com, anthony@...emonkey.ws
Subject: Re: [PATCH RFC V2 0/5] Separate consigned (expected steal) from
 steal time.

On Wed, 2012-10-17 at 21:14 +0400, Glauber Costa wrote:
> On 10/17/2012 06:23 AM, Michael Wolf wrote:
> > 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.  To ease the confusion this patch set
> > adds the idea of consigned (expected steal) time.  The host will separate
> > the consigned time from the steal time.  The consignment limit passed to the
> > host will be the amount of steal time expected within a fixed period of
> > time.  Any other steal time accruing during that period will show as the
> > traditional steal time.
> > 
> > TODO:
> > * Change native_clock to take params and not return a value
> > * Change update_rq_clock_task
> > 
> > Changes from V1:
> > * Removed the steal time allowed percentage from the guest
> > * Moved the separation of consigned (expected steal) and steal time to the
> >   host.
> > * No longer include a sysctl interface.
> > 
> 
> You are showing this in the guest somewhere, but tools like top will
> still not show it. So for quite a while, it achieves nothing.
> 
> Of course this is a barrier that any new statistic has to go through. So
> while annoying, this is per-se ultimately not a blocker.
> 
> What I still fail to see, is how this is useful information to be shown
> in the guest. Honestly, if I'm in a guest VM or container, any time
> during which I am not running is time I lost. It doesn't matter if this
> was expected or not. This still seems to me as a host-side problem, to
> be solved entirely by tooling.
> 

What tools like top and vmstat will show is altered.  When I put time in
the consign bucket it does not show up in steal.  So now as long as the
system is performing as expected the user will see 100% and 0% steal.  I
added the consign field to /proc/stat so that all time accrued in the
period is accounted for and also for debugging purposes.  The user wont
care about consign and will not see it.  

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