Messages in this thread | | | Date | Thu, 13 Nov 2008 11:02:04 +0100 | From | "Frédéric Weisbecker" <> | Subject | Re: [PATCH 2/2] tracing/function-return-tracer: Call prepare_ftrace_return by registers |
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2008/11/13 Ingo Molnar <mingo@elte.hu>: > on a related note. > > Frederic, it would be nice to fine-tune the tracer output to convey > the callgraph information more clearly. Here's a mockup of a good > default output: > > getnstimeofday() { > set_normalized_timespec() { > clocksource_read() { > acpi_pm_read() ( 1547 ns) > } clocksource_read() ( 1951 ns) > } set_normalized_timespec() ( 2200 ns) > } getnstimeofday() ( 2354 ns) > > [...]
Oh yes. That would be fine. I thought such thing would be better to do in post-processing. But I wonder a bit about this, I explain why below.
> Such output would be _very_ nice and intuitive to have. Developers > would love it instantly. Note its C-ish syntax - that is obviously the > easiest to parse for kernel developers.
That's right, it's much more better for the eyes. I didn't want to output such a disposition from the kernel because I thought that would result in too much strings work from kernel-space. But actually, as you suggest, if I append a depth field in the trace that could be easy and not so costly. I just have a last thought about post-processing parsing. Would it make it harder for that? Why not a flag that could be set through iter_ctrl (which has changed its name yesterday) and that could let the user to choose its output? That's where I renew my proposition to make the tracers able to propose custom flags for this file with a new callback such as tracer_ctrl, or tracer_opt.
After all perhaps an indented output would be better to build a tree of calls from parsing. And the current output would be better to build stats about return values and/or cost.
> and note how natural it will be in the future to embellish certain > function calls in the above trace, for example with function > arguments: > > clocksource_read("acpi_pm") { > > i'd suggest to hide the offset bit of the ksym (like the mockup does > it - unless a tracing_option is set for more verbose symbol output). > For these traces it's almost always useless and the context tells us > in 99% of the cases where a function got called.
I think it remains useful when a function calls one other in differents code paths. But as you say, why not set it through a flag.
> Easiest would be to add a depth field to the trace entry as well, to > make sure we get the right depth in the end, even if we somehow mix up > the trace entries.
Yeah, that's good! I will just have to output "\t" * depth to have the correct indentation.
> We could also trace function entry and exit separately, and > post-process the call stack (and the cost) during trace output > formatting - not during tracing. > > Hm?
Yes I thought about that. But with a bit post-processing, we could retrieve the result of the normal function tracing through the "return tracing" traces... I guess...
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