linux-kernel - Re: [RFC] [PATCH 7/7] Ftrace plugin for Uprobes

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Date:	Wed, 13 Jan 2010 16:58:23 -0500
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	rostedt@...dmis.org
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	utrace-devel <utrace-devel@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 7/7] Ftrace plugin for Uprobes

Steven Rostedt wrote:
> On Tue, 2010-01-12 at 05:54 +0100, Frederic Weisbecker wrote:
> 
>> Now what if I want to launch ls and want to profile a function
>> inside. What can I do with a trace event. I can't create the
>> probe event based on a pid as I don't know it in advance.
>> I could give it the ls cmdline and it manages to activate
>> on the next ls launched. This is racy as another ls can
>> be launched concurrently.
> 
> You make a wrapper script:
> 
> #!/bin/sh
> <add probe to ls with pid> $$
> exec $*
> 
> I do this all the time to limit the function tracer to a specific app.
> 
> #!/bin/sh
> echo $$ > /debug/tracing/set_ftrace_pid
> echo function > /debug/tracing/current_tracer
> exec $*

I recommend you to add below line at the end of the script,
from my experience. :)

echo nop > /debug/tracing/current_tracer

Thank you,


-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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