linux-kernel - Re: [PATCH v9 3.2 7/9] tracing: uprobes trace

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Date:	Tue, 17 Jan 2012 13:21:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>, Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Roland McGrath <roland@...k.frob.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Anton Arapov <anton@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v9 3.2 7/9] tracing: uprobes trace_event interface


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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