Re: Flight recorder mode

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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 hyb=
rid
>>>> one) of LTTng. I originally expected that this mode means:
>>>>
>>>>  1. Fixed set of buffers, older data will be overwritten on wrap-aro=
und
>>>>  2. Limited size of trace files
>>>>
>>>> While 1. seems to be true, 2. is neither what I observe in the outpu=
t
>>>> directory (flight-cpu_* get larger and larger) nor what I can find i=
n
>>>> 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.
>>
>=20
> Hrm, or do I recall doing documentaion I haven't done, let's see :)
>=20
> Ah, it's in a mailing list, not in the documentation yet :
>=20
> http://osdir.com/ml/linux.kernel.tracing/2006-09/msg00015.html
>=20
> It explains how to use the hybrid mode.  I'll cut'n'paste it at the end=

> of the quickstart guide.
>=20
> 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

Thanks!
Jan


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