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Date: Tue, 16 Nov 2010 18:38:23 +0200
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [RFC][PATCH v2 4/7] taskstats: Add per task steal time accounting
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
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>
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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.