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

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Date:	Fri, 14 Jan 2011 12:22:37 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Franck Bui-Huu <vagabon.xyz@...il.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

(2011/01/14 4:42), Franck Bui-Huu wrote:
 Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> writes:
> 
>> (2011/01/13 19:20), Franck Bui-Huu wrote:
>>> From: Franck Bui-Huu <fbuihuu@...il.com>
>>>
>>> It should be more usefull to get the full location of the function
>>
>>> (absolute line number + full path) instead of repeating the name of
>>> the function and the start line number given by the command line.
>>>
>>> So we had before:
>>>
>>>    $ perf probe -L schedule | head -n3
>>>    <schedule:0>
>>>          0  asmlinkage void __sched schedule(void)
>>>          1  {
>>>
>>> and now we get:
>>>
>>>    $ perf probe -L schedule | head -n3
>>>    </usr/src/debug/kernel-2.6.35.fc14/linux-2.6.35.x86_64/kernel/sched.c:3813>
>>>          0  asmlinkage void __sched schedule(void)
>>>          1  {
>>
>> Indeed, it could be useful for users to see where the function is...
>>
>> However, I think that should be optional, because the output lines
>> have the relative line numbers from the function, and those numbers
>> are important for users who want to probe a specific line by using
>> function relative line numbers. e.g. "schedule:10"
>>
>> And with that option, I'd suggest to show absolute line numbers on each line.
>>
>>   $ perf probe -L schedule:0-1 --by-source
>>   </usr/src/debug/kernel-2.6.35.fc14/linux-2.6.35.x86_64/kernel/sched.c:3813>
>>      3813  asmlinkage void __sched schedule(void)
>>      3814  {
>>
>> Or, just show source file as an additional information.
>>
>>   $ 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  {
>>
>> I just would like to keep the consistency of the output/input format.
> 
> Well, for consistency, I thought that the additional information (given
> inside angle brackets) should always be the same: a full path and an
> absolute line number which clearly identify which source file perf-probe
> is listing.

No, that is NOT an additional information. That indicates from where those
lines are started, and also gives you a hint how you can specify the
actual probe point. For example,

$ perf probe -L schedule:10
<schedule:10>
     10         rq = cpu_rq(cpu);
     11         rcu_note_context_switch(cpu);
     12         prev = rq->curr;

this indicates the lines started from 10th line of schedule(), and
if you want to put a new event on "prev = rq->curr;" line, you
just need to say "perf probe schedule:12"

$ perf probe -L kernel/sched.c:4077
</home/mhiramat/ksrc/linux-2.6-tip/kernel/sched.c:4077>
   4077         rq = cpu_rq(cpu);
   4078         rcu_note_context_switch(cpu);
   4079         prev = rq->curr;

And this also gives you a hint to say (just copy & paste)
"perf probe /home/mhiramat/ksrc/linux-2.6-tip/kernel/sched.c:4079"

Since perf probe also accepts FUNC@SRC:RLN, my suggestion
also keeps that rule.
---
  $ 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  {
---

Thank you,

-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com>
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