linux-kernel - Re: [PATCH -tip tracing/kprobes 0/9] tracing/kprobes, perf: perf probe and kprobe-tracer bugfixes

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Date:	Mon, 19 Oct 2009 18:54:19 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Mike Galbraith <efault@....de>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>
Subject: Re: [PATCH -tip tracing/kprobes 0/9] tracing/kprobes, perf: perf
 	probe and kprobe-tracer bugfixes

Masami Hiramatsu wrote:
> Ingo Molnar wrote:
>> For example you might want to probe the point within schedule that calls
>> switch_mm() - this could be done via:
>>
>>    perf probe schedule@...tch_mm
>>
>> Or the point where 'next' gets assigned? Sure, you dont need to even
>> open the editor, if you know the rough outline of the function you can
>> probe it via:
>>
>>    perf probe schedule@...xt ='
>>
>> Note that i was able to specify both probes without having opened an
>> editor - just based on the general knowledge of the scheduler.
> 
> It may be useful for return probe too :-)
> 
>  perf probe schedule@...urn

Hmm, IMHO,

>>    perf probe schedule@...tch_mm

might be confused as 'probe schedule() called from switch_mm()'.

BTW, there might be several local/inline functions which have
same name.
I think we'd better provide a syntax for solving this issue.
And current syntax uses @ for this purpose as below.

 perf probe localfunc@...e

Maybe, we still can use % for special matching,

 perf probe schedule%switch_mm

These can be combined with each other, as below.

 perf probe schedule@...nel/sched.c%switch_mm

Or, supporting lazy string pattern matching
 (reusing glob matching in ftrace?)

 perf probe schedule:'switch_mm(*);'

Just my thought.

Thank you,

-- 
Masami Hiramatsu

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

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

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