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

From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Avi Kivity <avi@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Michael Holzheu <holzheu@linux.vnet.ibm.com>,
	Shailabh Nagar <nagar1234@in.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Venkatesh Pallipadi <venki@google.com>,
	Suresh Siddha <suresh.b.siddha@intel.com>,
	Ingo Molnar <mingo@elte.hu>, Oleg Nesterov <oleg@redhat.com>,
	John stultz <johnstul@us.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Balbir Singh <balbir@linux.vnet.ibm.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Roland McGrath <roland@redhat.com>,
	linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
	"jeremy.fitzhardinge" <jeremy.fitzhardinge@citrix.com>
Subject: Re: [RFC][PATCH v2 4/7] taskstats: Add per task steal time accounting
Date: Tue, 16 Nov 2010 17:43:26 +0100	[thread overview]
Message-ID: <1289925806.2109.628.camel@laptop> (raw)
In-Reply-To: <4CE2B37F.8050808@redhat.com>

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.