linux-kernel - Re: [RFC][PATCH v2 4/7] taskstats: Add per task steal time accounting

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Date:	Tue, 16 Nov 2010 17:43:26 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Avi Kivity <avi@...hat.com>
Cc:	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Shailabh Nagar <nagar1234@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Venkatesh Pallipadi <venki@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com>,
	John stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
	"jeremy.fitzhardinge" <jeremy.fitzhardinge@...rix.com>
Subject: Re: [RFC][PATCH v2 4/7] taskstats: Add per task steal time
 accounting

On Tue, 2010-11-16 at 18:38 +0200, Avi Kivity wrote:
> On 11/16/2010 05:45 PM, Peter Zijlstra wrote:
> >
> >>> In fact, kvm seems to already have these tracepoints: kvm_exit/kvm_entry
> >>> and it has a separate excplicit hypercall tracepoint as well:
> >>> kvm_hypercall.
> >> But the kvm tracepoints are used when Linux is the hypervisor, no? For our
> >> situation that would be a tracepoint in z/VM - or the equivalent. This is
> >> out of scope of this patch.
> > Ah crud, you might be right.. Avi could a kvm guest generate events on
> > vcpu enter/exit?
> 
> No.  Hypercalls are voluntary and known, but most exits are involuntary 
> and unknown to the guest.  Any memory access can generate a page fault, 
> and any host interrupt will exit the guest.

Right, but we could not make the guest jump to a special stub on vcpu
enter? I guess we could simply because we have the hypervisor under
control.
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