Messages in this thread | | | Date | Tue, 20 Oct 2009 08:43:34 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH -tip tracing/kprobes 0/9] tracing/kprobes, perf: perf probe and kprobe-tracer bugfixes |
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* 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
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