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

[Mathieu Desnoyers]

* srikanth krishnakar (skrishnakar at gmail.com) wrote:
> Hello Mathieu,
> 
> Thanks a lot for your quick response !!
> 
> If i interpret your pointers correctly, then I understand,
> destroying+Appending trace result to previously destroyed trace session will
> not write matching meta-data to old channels, right ? which further results
> in difference in event sizes !
> 
> So correcting my execution script :
> 
> ###################################
> #!/bin/bash
> 
> mount -t debugfs debugfs /mnt/debug
> 
> ltt-armall
> 
> lttctl -C -w /home/root/trace1 trace1
> 
-C is for "create and start".

> lttctl -s trace1

so -s (start) is redundant. See lttctl --help.

> sleep 2
> 
> lttctl -p trace1
> 
> #lttctl -D trace1  # Pause and destroy a trace named trace1 and
> *<<<<< Eliminated
> the Destroy operation *
> sleep 10
> 
> lttctl -C trace1 -w  /home/root/trace1 *-a*    *<<< Retain append option for
> continuation with existing data*

-C will likely fail here, because you are trying to "create" an already
existing trace session.

Try lttctl -s   here instead.

Note that given that you do not destroy the trace session, you don't
need to start lttd again, because it will still be listening on the file
descriptors.

What are you trying to achieve exactly ?

Thanks,

Mathieu

> 
> lttctl -s trace1
> sleep 2
> 
> lttctl -p trace1
> 
> lttctl -D trace1
> 
> ltt-disarmall
> 
> lttv -m textDump -t /home/root/trace1
> ###################################
> 
> Does it looks OK ? Or still needs correction ?
> 
> And also one more small doubt regarding difference among '-c' && '-C'
> options, any significant changes that result after swapping these ?
> 
> Thanks & Regards
> -Srikant
> ----------
> 
> On Tue, Dec 21, 2010 at 12:57 AM, Mathieu Desnoyers <
> mathieu.desnoyers at polymtl.ca> wrote:
> 
> > * 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
> >
> 
> 
> 
> -- 
> "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