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Date: Tue, 17 Jan 2012 13:21:33 +0100
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH v9 3.2 7/9] tracing: uprobes trace_event interface
Message-ID: <20120117122133.GB4959@elte.hu>
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To: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>, Arnaldo Carvalho de Melo <acme@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, LKML <linux-kernel@vger.kernel.org>, Linux-mm <linux-mm@kvack.org>, Andi Kleen <andi@firstfloor.org>, Christoph Hellwig <hch@infradead.org>, Steven Rostedt <rostedt@goodmis.org>, Roland McGrath <roland@hack.frob.com>, Thomas Gleixner <tglx@linutronix.de>, Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>, Arnaldo Carvalho de Melo <acme@infradead.org>, Anton Arapov <anton@redhat.com>, Ananth N Mavinakayanahalli <ananth@in.ibm.com>, Jim Keniston <jkenisto@linux.vnet.ibm.com>, Stephen Rothwell <sfr@canb.auug.org.au>


Have you tried to use 'perf probe' to achieve any useful 
instrumentation on a real app?

I just tried out the 'glibc:free' usecase and it's barely 
usable.

Firstly, the recording very frequently produces overruns:

 $ perf record -e probe_libc:free -aR sleep 1
 [ perf record: Woken up 169 times to write data ]
 [ perf record: Captured and wrote 89.674 MB perf.data (~3917919 samples) ]
 Warning:Processed 1349133 events and lost 1 chunks!

Using -m 4096 made it work better.

Adding -g for call-graph profiling caused 'perf report' to lock 
up:

  perf record -m 4096 -e probe_libc:free -agR sleep 1
  perf report
  [ loops forever ]

I've sent a testcase to Arnaldo separately. Note that perf 
report --stdio appears to work.

Regular '-e cycles -g' works fine, so this is a uprobes specific 
bug.

Thanks,

	Ingo

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