Re: Flight recorder mode

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* 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?
> >>
> >=20
> > 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).
>=20
> 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.
>=20

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.

Mathieu

> Jan
>=20



--=20
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68

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