linux-kernel - ftrace/perf

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Message-ID: <4C7E11E5.1040402@redhat.com>
Date:	Wed, 01 Sep 2010 11:42:13 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	kvm-devel <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: ftrace/perf_event leak

  I recently added perf_event support to kvm_stat, to display kvm 
tracepoints as statistics (I'd like to fold this to tools/perf 
eventually, but that's another story).  However I'm seeing a resource 
leak - after I quit the tool, there are quite a few references into the 
kvm module:

   kvm_intel              43655  0
   kvm                   272984  269 kvm_intel

The tool is just a python script that reads 
/sys/kernel/debug/tracing/events/kvm to find out which events are 
available, uses perf_event_open() to create one group per cpu to which a 
lot of events are attached.  The only special thing I can think of is 
that we use an ioctl to attach a filter to many perf_event descriptors.

You can find the source at 
http://git.kernel.org/?p=virt/kvm/qemu-kvm.git;a=blob_plain;f=kvm/kvm_stat;hb=5bd5f131b50cb373ff4e2a3632c6dad00a1f0b55.  
All it needs are the kvm modules loaded; no need to actually run a 
guest.  Run as root.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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