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

[Ingo Molnar <mingo@elte.hu>]

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

[...]
>
> I think absolute and relative line modes are not colliding/contending 
> at all but actually fit two different needs.

Definitely so.

> - absolute is nice when you are lonely doing kernel debugging.
>   (can be expanded at will once you imagine user probes)
>   You are stuck in your code editor, trying to figure out the
>   origin of your problem and then you think it would be nice
>   to set a probe in branch 1 and in branch 2 inside func_foo().
>   Then you already have absolute lines and relying in
>   perf probe --list func_foo() to resolve an absolute line into
>   a relative one is a very undesired middle step.

Of course - absolute numbers definitely rule for everything that works 
on a whole-file basis. (I'd argue that if you do that from an editor 
then you want a short macro that just sets a probe there - much like a 
breakpoint. Such an editor macro would want to use absolute numbers.))

> - relative is nice in some other cases. When you already have
>   the function target in mind, you even don't need to check your
>   editor, just a quick check to this command and get the relative
>   line. But also when you want to transmit a probe reference
>   in a mailing list because of its better lifetime.

also useful for command line workflows: 'perf probe --list' output - i 
think we users to generate func_symbol+rel_position kind of probes.

Plus a relative position is more intuitive as well. If you see 
'schedule+10' versus 'schedule+102', you'll know it immediate that the 
first one is early in the function while the second one is near the end.

If you see 'schedule@2465' versus 'schedule@2555' that kind of 'where in 
the function is the probe, roughly' subjective impression is lost.

	Ingo