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SubjectRe: [PATCH] perf-probe: make "perf-probe -L <function>" display the absolute path and absolute line number
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Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> writes:

> (2011/01/14 4:42), Franck Bui-Huu wrote:

[...]

>> 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

But this indication is currently not enough, it's too ambiguous to be
usefull:

<schedule:10>

there might be several 'schedule()' functions inside the kernel, also we
don't know which kernel tree is used.

BTW, if there're several 'do_something' functions defined inside the
kernel, what is the behaviour of:

$ perf probe do_something

Does it set a probe to all 'do_something' functions ? I don't think it's
documented.

> , 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

but I'm not sure it's really usefull since you've asked for it when
invoking perf-probe so it seems to be redundant.

> if you want to put a new event on "prev = rq->curr;" line, you just
> need to say "perf probe schedule:12"

yes and this patch doesn't change that, does it ?

> $ 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)

No copy & paste in my case, I just reuse the shell history. This is the
reason why I didn't understand your suggestion.

So to get back to my initial suggestion and with this patch applied:

$ perf probe -L schedule:10-15
</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);
12 prev = rq->curr;
13 switch_count = &prev->nivcsw;

15 release_kernel_lock(prev);

I know exactly which bit of code I'm looking at, and to put a probe I
can still simply do (without any copy and paste):

$ perf probe schedule:12

I still use the function name of the probe and the relative line number
showed by perf-probe.

For probe specified by filename:

$ perf probe -L kernel/sched.c:3823-3826
</usr/src/debug/kernel-2.6.35.fc14/linux-2.6.35.x86_64/kernel/sched.c:3823>
3823 rq = cpu_rq(cpu);
3824 rcu_note_context_switch(cpu);
3825 prev = rq->curr;
3826 switch_count = &prev->nivcsw;

now to set a probe, I would do:

$ perf probe kernel/sched.c:3825

I still use the linenum showed by perf-probe, and the additional
information is always consistent and still usefull since it shows which
tree perf-probe is using.

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),
then this patch is wrong.

Thanks
--
Franck


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