[ltt-dev] LTTng kernel tracing with -a (append) feature

[Mathieu Desnoyers]

* srikanth krishnakar (skrishnakar at gmail.com) wrote:
> Hello Mathieu,
> 
> I am trying to test the append functionality of the ltt-control :
> 
> ltt-control : 0.79
> lttv-0.12.31
> Linux-2.6.32.9
> 
> #############################################
> 
> #!/bin/sh
> mount -t debugfs debugfs /mnt/debug
> *ltt-armall*
> *
> *
> *lttctl -C -w  /home/root/trace1 trace1*
> *
> *
> *lttctl -s trace1*
> sleep 2
> 
> *lttctl -p trace1*
> *
> *
> # Pause and destroy a trace named trace1 and

"-a" will not work if you stop+destroy a trace session and try appending
to the saved trace from a new trace session. The typical use-case is to
stop tracing (keeping the trace session alive), and then later on start
tracing again (within the same trace session), and there use the -a
switch to append to the existing trace files.

The problem is that the metadata (event IDs, event sizes, etc) are
supposed to be invariant across a whole trace session, but by appending
to the old trace files, you are combining two trace sessions together
with conflicting metadata.

Thanks,

Mathieu


> *lttctl -D trace1*
> 
> *lttctl -C trace1 -w  /home/root/trace1 -a                <<<<< Appending
> trace to existing one*
> *
> *
> *lttctl -s trace1*
> sleep 2
> 
> *lttctl -p trace1*
> *
> *
> *lttctl -D trace1*
> *
> *
> *ltt-disarmall*
> 
> *lttv -m textDump -t /home/root/trace1*
> *
> *
> *###########################################*
> 
> 
> Executing the above steps without  *'-a'* (append) options works perfectly
> and i am able to get the trace output after dumping. But the problem lies in
> when I try to execute with '-a' (append) feature, then the error displayed
> is difference in kernel event sizes and unable to dump the ouput
> 
> --------------------------------------------------------------------------------
> ** ERROR **: Kernel/LTTV event size differs for event timer_set: kernel 11,
> LTTV 12
> aborting...
> /usr/bin/lttv: line 15:  1516 Aborted                 $0.real $*
> --------------------------------------------------------------------------------
> 
> Is there anything missing or am i running out of process that needs to be
> followed to obtain the appended trace result ??
> 
> Is there any info in LTTng user manual that shows the steps to follow for
> using append feature of LTT-CONTROL in kernel tracing ?
> 
> Thanks in advance !!!
> -S
> 
> 
> -- 
> "The Good You Do, The Best You GET"
> 
> Regards
> Srikanth Krishnakar
> **********************

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com