On 2/25/13 3:18 AM, Stefan Hajnoczi wrote:
On Fri, Feb 22, 2013 at 11:34:27AM -0500, Mohamad Gebai wrote:
I am tracing kvm using perf and I am analyzing the sequences of kvm_entry and
kvm_exit tracepoints.
I noticed that during the boot process of a VM, there are a lot more (2 to 3 as
many times) kvm_entry event than there are kvm_exit. I tried looking around but
didn't find anything that explains this. Is this missing instrumentation? Or
what other path does kvm take that doesn't generate a kvm_exit event?
Gleb Natapov noticed something similar when playing with the perf script
I posted here:
http://permalink.gmane.org/gmane.comp.emulators.kvm.devel/104181
Have you tried using perf kvm stat? It is really easy to add a
flag/option to dump individual analysis points with the stats summary at
the end - or only dump data points greater than some threshold.
Latest version for the 'live mode' can be found here:
https://github.com/dsahern/linux/tree/perf-kvm-live-3.8
Perhaps there is a code path that is missing trace_kvm_exit().
I have been playing with the live mode a bit lately. I'll add a debug to
note 2 consecutive entry events without an exit -- see if it sheds some
light on it.
David
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