linux-kernel - Re: [PATCH] perf-probe: make "perf-probe -L <function>" display the absolute path and absolute line number

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Message-ID: <m3aaj3ntwo.fsf@gmail.com>
Date:	Fri, 14 Jan 2011 20:53:59 +0100
From:	Franck Bui-Huu <vagabon.xyz@...il.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	lkml <linux-kernel@...r.kernel.org>,
	2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCH] perf-probe: make "perf-probe -L <function>" display the absolute path and absolute line number

Hi Masami,

Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> writes:

> (2011/01/14 18:03), Franck Bui-Huu wrote:
>> But if you think it should be used to hint for a probe point syntax,
>> (you'll probably use copy & paste since it uses absolute path name),
>
> Not only for copy&paste, but also for avoiding confusion.
> Please imagine that user see this output.
>
>    </usr/src/debug/kernel-2.6.35.fc14/linux-2.6.35.x86_64/kernel/sched.c:3823>
>         10         rq = cpu_rq(cpu);
>         11         rcu_note_context_switch(cpu);
>
> "Why the definition line number and starting line number are different?"
> "How I can put a probe?  sched.c:3823 ... + 10??"

No because if you see relative line number, then the user had used the
following command:

   $ perf probe -L schedule

so I would assume that his next add command would still use a function
name:

   $ perf probe schedule:10

> 
> "Or, it's just buggy! report it!"
>
> I don't want this.
>
>> then this patch is wrong.
>
> Yeah, but just a _bit_. Basically, I agree with your idea of showing
> actual path of the function, because, indeed, perf-probe just shows
> the first one even if there are many same-name functions.
>
> So, here, I had suggested an enhancement idea;
>
>   $ perf probe -L schedule:0-1
>   <schedule@...r/src/debug/kernel-2.6.35.fc14/linux-2.6.35.x86_64/kernel/sched.c:0>
>         0  asmlinkage void __sched schedule(void)
>         1  {
>
> This is acceptable, because it shows which function you see and
> it also gives you how you can specify a probe point on a function
> line.

I can understand your point, but I'm currently not seeing it as a hint
for a probe point syntax.

But you're a far more experienced user than I am so you're probably
right.

Thanks
-- 
		Franck
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