Re: Flight recorder mode

* Jan Kiszka ([email protected]) wrote:
> Jan Kiszka wrote:
> > Mathieu Desnoyers wrote:
> >> * Jan Kiszka ([email protected]) wrote:
> >>> Mathieu Desnoyers wrote:
> >>>> * Jan Kiszka ([email protected]) wrote:
> >>>>> Hi,
> >>>>>
> >>>>> I'm trying to understand the flight recorder mode (including the hybrid
> >>>>> one) of LTTng. I originally expected that this mode means:
> >>>>>
> >>>>>  1. Fixed set of buffers, older data will be overwritten on wrap-around
> >>>>>  2. Limited size of trace files
> >>>>>
> >>>>> While 1. seems to be true, 2. is neither what I observe in the output
> >>>>> directory (flight-cpu_* get larger and larger) nor what I can find in
> >>>>> lttd's code. Intentionally?
> >>>>>
> >>>> Yep, see the other lttctl options and the quickstart guide to see how to
> >>>> spawn one lttd for the "normal" channels and a different one for the
> >>>> flight recorder channels (should be done after you stop tracing).
> >>> Sorry, /me is too blind: The quickstart guide is not mentioning flight
> >>> recorder or hybrid mode, and also lttctl --help gives me no hint what
> >>> pattern to apply for achieving limited trace file sizes.
> >>>
> >> Hrm, or do I recall doing documentaion I haven't done, let's see :)
> >>
> >> Ah, it's in a mailing list, not in the documentation yet :
> >>
> >> http://osdir.com/ml/linux.kernel.tracing/2006-09/msg00015.html
> >>
> >> It explains how to use the hybrid mode.  I'll cut'n'paste it at the end
> >> of the quickstart guide.
> >>
> >> There is not trace file size limit you can give to lttctl nor lttd. You
> >> can only specify the buffer size. The idea is that you can decide at
> >> which moment you want to take you flight recorder "snapshot" by running
> >> lttctl -f at the correct moment.
> > 
> > OK, -EBRAINSUSPENDED, you just woke it up again:
> > 
> > lttctl -b -n mytrace -m flight -l <debugfs>/ltt
> > <run application>
> > <when something happened:>
> > lttctl -f -n mytrace -t <trace-out> -l <debugfs>/ltt
> 
> Hmm, in fact this won't fly yet. It looks like I need the hybrid mode,
> because flight recorder traces generated like above are lacking some
> basic information (stuff under /control I guess) to make lttv happy.
> 
> That leaves me with a (for now) acceptable tracing procedure via hybrid
> traces. But I'm still lacking some howto for pure flight recorder
> traces. Any hints still appreciated... :)
> 

Hrm, LTTV should be able to cope with the missing control information.
The only tracefiles that needs to be complete are the facilities
tracefiles.

What do you get when you start lttv on a flight recorder trace ?

> Jan
> 
> -- 
> Siemens AG, Corporate Technology, CT SE 2
> Corporate Competence Center Embedded Linux
> 

-- 
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
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