Re: [RFC] SystemTap future direction

[Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>]

Mark Wielaard wrote:
>>>> - Port SystemTap on the perf/ftrace but drop embedded-C support.
>>>>  This will enhance perf/ftrace to support enough flexible data
>>>>  filter/modifier (including fault injection feature). In this case,
>>>>  SystemTap scripts will handle the data in user-space (not on-line).
>>> I think the "not on-line" part is a bit of a showstopper. Since that
>>> kills the main idea of having powerful scriptable observability. Simple
>>> filters are too restrictive IMHO. It might be enough for simple
>>> profiling, where you analyze the data off-line afterwards. But that
>>> isn't an option for everybody (you need to store/push the data
>>> somewhere), and not very efficient some cases.
>> The efficiency is the key, and perf and systemtap aim to
>> different efficiency. SystemTap focuses on the efficiency of
>> transporting data, but perf focuses on the efficiency of
>> probing time. What they are trying to is reducing the overhead
>> of recording data to buffers, because it is less disturbance for
>> the performance of target processes.
> 
> Right. It just comes down to priorities of the different goals.
> Profiling (with offline analysis) versus scriptable tracing (with some
> debugging elements). But making either efficient will help both cases.
> We just have to be careful not to trade in one completely for the other,
> or we kill useful use cases at probing time.

Hmm, could you find any useful use-case of scriptable tracing (on-line)?
I know generally scriptable interface provides us great flexibility, but
does it have to be done on-line? I mean, perf already has scriptable
interface(python and perl) for off-line analysis. Why isn't that enough?

I just know that some complicated fault-injections are really useful example
of scriptable tracing on-line.

e.g.
http://ols.fedoraproject.org/OLS/Reprints-2008/tanaka-reprint.pdf

Thank you,

-- 
Masami HIRAMATSU
2nd Research Dept.
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com