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

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Date:	Mon, 18 Feb 2013 22:11:04 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Michael Wolf <mjw@...ux.vnet.ibm.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 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.

But yes, a description of the scenario that is being dealt with, with
details, is important.

> > 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.  Tthe steal time will only be altered
> > if hard limits (cfs bandwidth control) is used.  The period and the quota used
> > to separate the consigned time (expected steal) from the steal time are taken
> > from the cfs bandwidth control settings. Any other steal time accruing during
> > that period will show as the traditional steal time.
> 
> I'm also a bit confused here. steal time will then only account the
> cpu time lost due to quotas from cfs bandwidth control? Also what do
> you exactly mean by "expected steal time"? Is it steal time due to
> overcommitting minus scheduler quotas?
> 
> Thanks.
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